Income Taxes - Additional Information (Details) - USD ($) $ in Millions	3 Months Ended		6 Months Ended
	Jun. 30, 2018	Jun. 30, 2017	Jun. 30, 2018	Jun. 30, 2017
Income Tax Disclosure [Abstract]
Income tax expense (benefit)	$ 27	$ (8)	$ 52	$ 25
Net tax benefit related to acquisition charges	5		7
Net tax expense (benefit) for prior year tax adjustments	2	$ (50)	2	$ (49)
One time tax benefit			54
Reasonably possible change in unrecognized tax benefits	$ 7		$ 7