Investments (Net change in unrealized gains (losses) on investments) (Details) - USD ($) $ in Millions	12 Months Ended
	Dec. 31, 2018	Dec. 31, 2017	Dec. 31, 2016
Debt Securities, Available-for-sale [Line Items]
Total net change in unrealized gains on investments	$ (1,811)	$ 758	$ 224
Fixed maturity securities
Debt Securities, Available-for-sale [Line Items]
Total net change in unrealized gains on investments	(1,811)	728	225
Equity securities
Debt Securities, Available-for-sale [Line Items]
Total net change in unrealized gains on investments	0	32	(2)
Other
Debt Securities, Available-for-sale [Line Items]
Total net change in unrealized gains on investments	$ 0	$ (2)	$ 1