Income Taxes (Narrative) (Details) $ in Millions	3 Months Ended	12 Months Ended
	Dec. 31, 2017 USD ($)	Dec. 31, 2017 USD ($)
Income Tax Disclosure [Abstract]
Provisional adjustment of income tax benefit		$ 591
Foreign and state net operating loss carryforwards	$ 405	405
Change in valuation allowance		3
Provisional tax expense related to one-time repatriation	$ 5
Foreign tax		$ 7