Income Taxes (Impact of Accounting for the Enactment of the Tax Act) (Details) - USD ($) $ in Millions	3 Months Ended	12 Months Ended
	Dec. 31, 2017	Dec. 31, 2018	Dec. 31, 2017
Income Tax Disclosure [Abstract]
Revaluation of deferred tax balances		$ 1	$ (746)
One-time transition tax		5	57
Total provision (benefit) for income taxes impact	$ (689)	$ 6	$ (689)