Employee Stock and Savings Plans - Schedule of Additional Information Related to Stock Option and Restricted Stock Unit Activity (Details) - USD ($) $ in Millions	12 Months Ended
	Dec. 31, 2015	Dec. 31, 2014	Dec. 31, 2013
Disclosure of Compensation Related Costs, Share-based Payments [Abstract]
Total intrinsic value of stock options exercised	$ 123	$ 43	$ 27
Cash received from stock option exercises	35	33	32
Gross income tax benefit from stock option exercises	46	16	10
Fair value of restricted stock units upon vesting	$ 41	$ 35	$ 31