Investments Schedule of Gains and Losses on Equity and Other Investments (Details) - USD ($) $ in Millions	12 Months Ended
	Dec. 31, 2018	Dec. 31, 2017	Dec. 31, 2016
Gain (Loss) on Securities [Line Items]
Unrealized Gain (Loss) on Investments	$ (1,699)	$ 392	$ 184
Equity Securities [Member]
Gain (Loss) on Securities [Line Items]
Equity Securities, FV-NI, Realized Gain (Loss)	(59)
Unrealized Gain (Loss) on Investments	0	88	52
Other Investments [Member]
Gain (Loss) on Securities [Line Items]
Realized Investment Gains (Losses)	(5)	$ 0	$ 0
Accounting Standards Update 2016-01 [Member] | Equity Securities [Member]
Gain (Loss) on Securities [Line Items]
Equity Securities, FV-NI, Realized Gain (Loss)	(59)
Unrealized Gain (Loss) on Investments	(129)
Gain (Loss) on Sale of Investments	70
Accounting Standards Update 2016-01 [Member] | Other Investments [Member]
Gain (Loss) on Securities [Line Items]
Unrealized Gain (Loss) on Investments	(126)
Gain (Loss) on Sale of Investments	121
Realized Investment Gains (Losses)	(5)
Accounting Standards Update 2016-01 [Member] | Equity securities and other investments [Member]
Gain (Loss) on Securities [Line Items]
Unrealized Gain (Loss) on Investments	(255)
Gain (Loss) on Sale of Investments	191
Realized Investment Gains (Losses)	$ (64)