Goodwill and Other Intangible Assets - Changes in Goodwill and Other Intangible Assets (Details) $ in Millions	3 Months Ended
	Mar. 31, 2018 USD ($)
Goodwill and Other Intangible Assets [Roll Forward]
Amortizing Intangible Assets, Beginning Balance	$ 355
Finite-lived Intangible Assets Acquired	0
Amortizing Intangible Assets, Amortization expense	(16)
Amortizing Intangible Assets, Ending Balance	339
Goodwill, Beginning Balance	3,815
Goodwill, Other Increase (Decrease)	2
Goodwill, Ending Balance	3,817
Other Non-Amortizing Intangible Assets, Beginning Balance	1,254
Indefinite-lived Intangible Assets Acquired	4
Other Non-Amortizing Intangible Assets, Ending Balance	$ 1,258