Fair Value Measurements (Assets And Liabilities Recorded At Fair Value On A Nonrecurring Basis) (Details) - Nonrecurring - Level 3 - USD ($) $ in Millions |
Mar. 31, 2018 |
Dec. 31, 2017 |
|---|---|---|
| Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items] | ||
| Total assets at fair value | $ 106 | $ 116 |
| Commercial borrower | Domestic loans | ||
| Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items] | ||
| Loans | 102 | 111 |
| Commercial borrower | Commercial Mortgage Loans | Domestic loans | ||
| Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items] | ||
| Loans | $ 4 | $ 5 |