Debt (Narrative) (Details) $ in Millions |
3 Months Ended | 6 Months Ended | 12 Months Ended | |||
|---|---|---|---|---|---|---|
|
Dec. 31, 2015
USD ($)
|
Dec. 31, 2013
USD ($)
|
Jun. 30, 2016
USD ($)
|
Dec. 31, 2015
USD ($)
quarter
|
Dec. 31, 2014
USD ($)
|
Dec. 31, 2013
USD ($)
|
|
| Debt Instrument [Line Items] | ||||||
| Gain (loss) on extinguishment of debt | $ 0 | $ 0 | $ (178) | |||
| FHLB line of credit, maximum amount available | $ 7,000 | $ 7,000 | 7,000 | |||
| FHLB advances, line of credit | 500 | $ 900 | $ 500 | |||
| Three Month LIBOR | ||||||
| Debt Instrument [Line Items] | ||||||
| FHLB Advances, Interest Rate Reset Period (in months) | 3 months | 3 months | ||||
| FHLB Advances, Prepayment Notification Period (in months) | 3 months | 3 months | ||||
| FHLB Advances, Initial Lockout Period (in months) | 12 months | 12 months | ||||
| Federal Home Loan Bank Advances | ||||||
| Debt Instrument [Line Items] | ||||||
| Payments for Federal Home Loan Bank Advances | 375 | $ 2,900 | ||||
| Gain (loss) on extinguishment of debt | $ 3 | $ (178) | ||||
| Junior Subordinated Debt [Member] | ||||||
| Debt Instrument [Line Items] | ||||||
| Debt Instrument, Interest Payment Deferment Period | quarter | 16 | |||||