Fair Value Measurements - Financial Assets and Financial Liabilities Carried at Fair Value (Details) (USD $)
In Millions, unless otherwise specified
 3 Months Ended 12 Months Ended
Mar. 31, 2015
Dec. 31, 2014
Financial assets at fair value:    
Fixed maturities $ 19,141 $ 18,983
Equity securities 182 189
Short-term investments 172 163
Fair Value, Measurements, Recurring [Member]    
Financial assets at fair value:    
Fixed maturities 19,141 [1] 18,983 [2]
Equity securities 182 189
Subtotal 19,323 19,172
Short-term investments 172 163
Total financial assets at fair value, excluding separate accounts 20,481 20,294
Financial liabilities at fair value:    
Total financial liabilities at fair value 948 930
Run-off Settlement Annuity Business [Member] | Fair Value, Measurements, Recurring [Member]    
Financial liabilities at fair value:    
Net appreciation required to adjust future policy benefits for run-off settlement annuity business included in fixed maturities 817 756
Other derivatives [Member] | Fair Value, Measurements, Recurring [Member]    
Financial assets at fair value:    
Derivative assets 16 [3] 6 [4]
Financial liabilities at fair value:    
Derivative liabilities   1 [4]
Other derivatives [Member] | Designated as Hedging Instrument [Member] | Cash Flow Hedging [Member] | Fair Value, Measurements, Recurring [Member]    
Financial assets at fair value:    
Derivative assets 15 5
Financial liabilities at fair value:    
Derivative liabilities   1
Other derivatives [Member] | Designated as Hedging Instrument [Member] | Fair Value Hedging [Member] | Fair Value, Measurements, Recurring [Member]    
Financial assets at fair value:    
Derivative assets 1 1
Other derivatives [Member] | Non designated [Member] | Fair Value, Measurements, Recurring [Member]    
Financial assets at fair value:    
Derivative assets 0 0
Financial liabilities at fair value:    
Derivative liabilities   0
Guaranteed Minimum Income Benefit [Member]    
Financial liabilities at fair value:    
Percentage of GMIB exposure covered by retrocessional coverage 100.00% 100.00%
Number of external reinsurers 3 3
Guaranteed Minimum Income Benefit [Member] | Fair Value, Measurements, Recurring [Member]    
Financial assets at fair value:    
Derivative assets 970 [5] 953 [6]
Financial liabilities at fair value:    
Derivative liabilities 948 929
Federal government and agency [Member] | Fair Value, Measurements, Recurring [Member]    
Financial assets at fair value:    
Fixed maturities 923 954
State and local government [Member] | Fair Value, Measurements, Recurring [Member]    
Financial assets at fair value:    
Fixed maturities 1,832 1,856
Foreign government [Member] | Fair Value, Measurements, Recurring [Member]    
Financial assets at fair value:    
Fixed maturities 1,956 1,940
Corporate [Member] | Fair Value, Measurements, Recurring [Member]    
Financial assets at fair value:    
Fixed maturities 13,721 13,498
Mortgage-backed [Member] | Fair Value, Measurements, Recurring [Member]    
Financial assets at fair value:    
Fixed maturities 64 85
Other asset-backed [Member] | Fair Value, Measurements, Recurring [Member]    
Financial assets at fair value:    
Fixed maturities 645 650
Fair Value Inputs Level 1 [Member] | Fair Value, Measurements, Recurring [Member]    
Financial assets at fair value:    
Fixed maturities 258 [1] 290 [2]
Equity securities 34 61
Subtotal 292 351
Short-term investments 0 0
Total financial assets at fair value, excluding separate accounts 292 351
Financial liabilities at fair value:    
Total financial liabilities at fair value 0 0
Fair Value Inputs Level 1 [Member] | Other derivatives [Member] | Fair Value, Measurements, Recurring [Member]    
Financial assets at fair value:    
Derivative assets 0 [3] 0 [4]
Financial liabilities at fair value:    
Derivative liabilities   0 [4]
Fair Value Inputs Level 1 [Member] | Guaranteed Minimum Income Benefit [Member] | Fair Value, Measurements, Recurring [Member]    
Financial assets at fair value:    
Derivative assets 0 [5] 0 [6]
Financial liabilities at fair value:    
Derivative liabilities 0 0
Fair Value Inputs Level 1 [Member] | Federal government and agency [Member] | Fair Value, Measurements, Recurring [Member]    
Financial assets at fair value:    
Fixed maturities 258 290
Fair Value Inputs Level 1 [Member] | State and local government [Member] | Fair Value, Measurements, Recurring [Member]    
Financial assets at fair value:    
Fixed maturities 0 0
Fair Value Inputs Level 1 [Member] | Foreign government [Member] | Fair Value, Measurements, Recurring [Member]    
Financial assets at fair value:    
Fixed maturities 0 0
Fair Value Inputs Level 1 [Member] | Corporate [Member] | Fair Value, Measurements, Recurring [Member]    
Financial assets at fair value:    
Fixed maturities 0 0
Fair Value Inputs Level 1 [Member] | Mortgage-backed [Member] | Fair Value, Measurements, Recurring [Member]    
Financial assets at fair value:    
Fixed maturities 0 0
Fair Value Inputs Level 1 [Member] | Other asset-backed [Member] | Fair Value, Measurements, Recurring [Member]    
Financial assets at fair value:    
Fixed maturities 0 0
Fair Value Inputs Level 2 [Member] | Fair Value, Measurements, Recurring [Member]    
Financial assets at fair value:    
Fixed maturities 18,110 [1] 17,879 [2]
Equity securities 103 85
Subtotal 18,213 17,964
Short-term investments 172 163
Total financial assets at fair value, excluding separate accounts 18,401 18,133
Financial liabilities at fair value:    
Total financial liabilities at fair value 0 1
Fair Value Inputs Level 2 [Member] | Other derivatives [Member] | Fair Value, Measurements, Recurring [Member]    
Financial assets at fair value:    
Derivative assets 16 [3] 6 [4]
Financial liabilities at fair value:    
Derivative liabilities   1 [4]
Fair Value Inputs Level 2 [Member] | Guaranteed Minimum Income Benefit [Member] | Fair Value, Measurements, Recurring [Member]    
Financial assets at fair value:    
Derivative assets 0 [5] 0 [6]
Financial liabilities at fair value:    
Derivative liabilities 0 0
Fair Value Inputs Level 2 [Member] | Federal government and agency [Member] | Fair Value, Measurements, Recurring [Member]    
Financial assets at fair value:    
Fixed maturities 665 664
Fair Value Inputs Level 2 [Member] | State and local government [Member] | Fair Value, Measurements, Recurring [Member]    
Financial assets at fair value:    
Fixed maturities 1,832 1,856
Fair Value Inputs Level 2 [Member] | Foreign government [Member] | Fair Value, Measurements, Recurring [Member]    
Financial assets at fair value:    
Fixed maturities 1,953 1,936
Fair Value Inputs Level 2 [Member] | Corporate [Member] | Fair Value, Measurements, Recurring [Member]    
Financial assets at fair value:    
Fixed maturities 13,371 13,105
Fair Value Inputs Level 2 [Member] | Mortgage-backed [Member] | Fair Value, Measurements, Recurring [Member]    
Financial assets at fair value:    
Fixed maturities 63 84
Fair Value Inputs Level 2 [Member] | Other asset-backed [Member] | Fair Value, Measurements, Recurring [Member]    
Financial assets at fair value:    
Fixed maturities 226 234
Fair Value Inputs Level 3 [Member] | Fair Value, Measurements, Recurring [Member]    
Financial assets at fair value:    
Fixed maturities 773 [1] 814 [2]
Equity securities 45 43
Subtotal 818 857
Short-term investments 0 0
Total financial assets at fair value, excluding separate accounts 1,788 1,810
Financial liabilities at fair value:    
Total financial liabilities at fair value 948 929
Fair Value Inputs Level 3 [Member] | Run-off Settlement Annuity Business [Member] | Fair Value, Measurements, Recurring [Member]    
Financial liabilities at fair value:    
Net appreciation required to adjust future policy benefits for run-off settlement annuity business included in fixed maturities 71 65
Fair Value Inputs Level 3 [Member] | Other derivatives [Member] | Fair Value, Measurements, Recurring [Member]    
Financial assets at fair value:    
Derivative assets 0 [3] 0 [4]
Financial liabilities at fair value:    
Derivative liabilities   0 [4]
Fair Value Inputs Level 3 [Member] | Guaranteed Minimum Income Benefit [Member] | Fair Value, Measurements, Recurring [Member]    
Financial assets at fair value:    
Derivative assets 970 [5] 953 [6]
Financial liabilities at fair value:    
Derivative liabilities 948 929
Fair Value Inputs Level 3 [Member] | Federal government and agency [Member] | Fair Value, Measurements, Recurring [Member]    
Financial assets at fair value:    
Fixed maturities 0 0
Fair Value Inputs Level 3 [Member] | State and local government [Member] | Fair Value, Measurements, Recurring [Member]    
Financial assets at fair value:    
Fixed maturities 0 0
Fair Value Inputs Level 3 [Member] | Foreign government [Member] | Fair Value, Measurements, Recurring [Member]    
Financial assets at fair value:    
Fixed maturities 3 4
Fair Value Inputs Level 3 [Member] | Corporate [Member] | Fair Value, Measurements, Recurring [Member]    
Financial assets at fair value:    
Fixed maturities 350 393
Fair Value Inputs Level 3 [Member] | Mortgage-backed [Member] | Fair Value, Measurements, Recurring [Member]    
Financial assets at fair value:    
Fixed maturities 1 1
Fair Value Inputs Level 3 [Member] | Other asset-backed [Member] | Fair Value, Measurements, Recurring [Member]    
Financial assets at fair value:    
Fixed maturities $ 419 $ 416
[1] Fixed maturities included $817 million of net appreciation required to adjust future policy benefits for the run-off settlement annuity business including $71 million of appreciation for securities classified in Level 3. See Note 8 for additional information.
[2] Fixed maturities included $756 million of net appreciation required to adjust future policy benefits for the run-off settlement annuity business including $65 million of appreciation for securities classified in Level 3. See Note 8 for additional information.
[3] Other derivative assets included $15 million of interest rate and foreign currency swaps qualifying as cash flow hedges and $1 million of interest rate swaps qualifying as fair value hedges. See Note 9 for additional information.
[4] Other derivative assets included $5 million of interest rate and foreign currency swaps qualifying as cash flow hedges and $1 million of interest rate swaps qualifying as fair value hedges. Other derivative liabilities reflected interest rate and foreign currency swaps qualifying as cash flow hedges. See Note 9 for additional information.
[5] The GMIB assets represent retrocessional contracts in place from three external reinsurers that cover the exposures on these contracts.
[6] The GMIB assets represented retrocessional contracts in place from three external reinsurers that cover the exposures on these contracts.