Goodwill and Other Intangible Assets - Amortization Expense (Details) - USD ($) $ in Millions	12 Months Ended
	Dec. 31, 2017	Dec. 31, 2016	Dec. 31, 2015
Goodwill and Intangible Assets Disclosure [Abstract]
Amortization of other intangible assets	$ 214	$ 207	$ 197
Finite-Lived Intangible Assets, Net, Amortization Expense, Fiscal Year Maturity [Abstract]
2018	191
2019	174
2020	171
2021	166
2022	$ 165