Investments - Unrealized Gains and Losses Relating to Equities (Details) - Equity securities $ in Millions |
3 Months Ended |
|---|---|
|
Mar. 31, 2018
USD ($)
| |
| Gain (Loss) on Investments [Line Items] | |
| Net losses recognized during the period on equity securities | $ (726) |
| Less: Net gains recognized during the period on equity securities sold | (1,881) |
| Unrealized losses recognized during the period on equity securities still held at the reporting date | $ (2,607) |