Fair Value Disclosures (Fair Value of Investments Measured at Net Asset Value) (Details) - USD ($) $ in Millions |
Mar. 31, 2016 |
Dec. 31, 2015 |
|---|---|---|
| Fair Value of Investments that Calculate Net Asset Value | ||
| Fair Value | $ 3,388 | $ 3,843 |
| Commitment | 584 | 670 |
| Private Equity Funds | ||
| Fair Value of Investments that Calculate Net Asset Value | ||
| Fair Value | 1,768 | 1,917 |
| Commitment | 467 | 538 |
| Real Estate Funds | ||
| Fair Value of Investments that Calculate Net Asset Value | ||
| Fair Value | 1,274 | 1,337 |
| Commitment | 113 | 128 |
| Long-short Equity Hedge Funds | ||
| Fair Value of Investments that Calculate Net Asset Value | ||
| Fair Value | 193 | 422 |
| Commitment | 0 | 0 |
| Fixed Income/Credit-Related Hedge Funds | ||
| Fair Value of Investments that Calculate Net Asset Value | ||
| Fair Value | 52 | 71 |
| Commitment | 0 | 0 |
| Event Driven Hedge Funds | ||
| Fair Value of Investments that Calculate Net Asset Value | ||
| Fair Value | 2 | 2 |
| Commitment | 0 | 0 |
| Multi-strategy Hedge Funds | ||
| Fair Value of Investments that Calculate Net Asset Value | ||
| Fair Value | 99 | 94 |
| Commitment | $ 4 | $ 4 |