Significant Accounting Policies - Additional Information (Details) - USD ($) $ in Millions	3 Months Ended	9 Months Ended
	Sep. 30, 2016	Sep. 30, 2016	Sep. 30, 2015	Jan. 01, 2016
New Accounting Pronouncements Or Change In Accounting Principle [Line Items]
Increase in cash flows from operating activities		$ 277	$ 339
Reduction in cash flows from financing activities		133	93
New Accounting Pronouncement, Early Adoption | ASU 2016-09
New Accounting Pronouncements Or Change In Accounting Principle [Line Items]
Increase in cash flows from operating activities			32
Reduction in cash flows from financing activities			$ 32
Reduction to retained earnings				$ 1
Recognition of net excess tax expense (benefit) in provision for income taxes	$ 1	$ (2)