Goodwill and Other Intangible Assets - Changes in Goodwill and Other Intangible Assets (Details) $ in Millions	6 Months Ended
	Jun. 30, 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	33
Amortizing Intangible Assets, Ending Balance	322
Goodwill, Beginning Balance	3,815
Goodwill, Other Increase (Decrease)	(1)
Goodwill, Ending Balance	3,814
Other Non-Amortizing Intangible Assets, Beginning Balance	1,254
Indefinite-lived Intangible Assets Acquired	(3)
Other Non-Amortizing Intangible Assets, Ending Balance	$ 1,251