Fair Value (Nonrecurring Fair Value Measurements) (Details) - Nonrecurring - USD ($) $ in Millions	12 Months Ended
	Dec. 31, 2018	Dec. 31, 2017	Dec. 31, 2016
Other limited partnership interests
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Investments, Fair Value Disclosure		$ 58	$ 96
Gains (Losses)		(65)	(64)
Other Assets
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Other Assets, Fair Value Disclosure	$ 0	0	0
Gains (Losses)	$ 0	$ 10	$ (30)