Fair Value Disclosures (Fund Interests Measured Based on Net Asset Value) (Details) - USD ($) $ in Millions |
Dec. 31, 2018 |
Dec. 31, 2017 |
|---|---|---|
| Measured Based on Net Asset Value | ||
| Carrying value | $ 2,582 | $ 2,564 |
| Commitment | 481 | 495 |
| Private Equity Funds | ||
| Measured Based on Net Asset Value | ||
| Carrying value | 1,374 | 1,674 |
| Commitment | 316 | 308 |
| Carrying Value of Nonredeemable Funds by Contractual Maturity | ||
| Less than 5 years | 707 | |
| 5-10 years | 642 | |
| Over 10 years | 25 | |
| Total | 1,374 | |
| Real Estate Funds | ||
| Measured Based on Net Asset Value | ||
| Carrying value | 1,105 | 800 |
| Commitment | 161 | 183 |
| Carrying Value of Nonredeemable Funds by Contractual Maturity | ||
| Less than 5 years | 618 | |
| 5-10 years | 440 | |
| Over 10 years | 47 | |
| Total | 1,105 | |
| Hedge Funds | ||
| Measured Based on Net Asset Value | ||
| Carrying value | 103 | 90 |
| Commitment | $ 4 | $ 4 |