Income Taxes - Narrative (Details) - USD ($) $ in Millions	12 Months Ended
	Dec. 31, 2017	Dec. 31, 2016	Dec. 31, 2015	Dec. 31, 2014
Income Tax Disclosure [Abstract]
Deferred tax benefit due to revaluation of deferred tax assets	$ 197
Provisional transition tax expense	454
Unrecognized tax benefits	94	$ 71	$ 63	$ 163
Unrecognized tax benefits that would impact effective tax rate	87	63	55
Maximum estimated income tax expense change in unrecognized tax benefit in the next 12 months	14
Interest expense for tax examination	3	2
Interest accrued for tax examination	$ 8	$ 5	$ 3