Investments (Gains and Losses Recognized on Equity Securities) (Details) - USD ($) $ in Millions	3 Months Ended		6 Months Ended
	Jun. 30, 2019	Jun. 30, 2018	Jun. 30, 2019	Jun. 30, 2018
Schedule of losses and gains related to equity securities [Line Items]
Net realized gains (losses) on financial instruments	$ 11	$ 4	$ 89	$ (22)
Equity Securities [Member]
Schedule of losses and gains related to equity securities [Line Items]
Net realized gains (losses) on financial instruments	13	(17)	92	(60)
Less: Net realized gains recognized on sale of equity securities during the period	(29)	(24)	(50)	(197)
Unrealized gains (losses) recognized on equity securities still held	$ (16)	$ (41)	$ 42	$ (257)