Stock-based Compensation (Details) - USD ($) $ / shares in Units, shares in Millions, $ in Millions	3 Months Ended
	Mar. 31, 2016	Mar. 31, 2015
Share-based Compensation [Abstract]
RSUs	$ 36	$ 38
Stock options	7	8
Stock-based compensation expense, before income taxes	43	46
Related tax benefit	(17)	(18)
Stock-based compensation expense, net of tax benefit	$ 26	$ 28
Number of RSUs granted during the period	3
Weighted average grant date fair value - RSUs	$ 45.74
Number of stock options granted during the period	2
Weighted average per unit exercise price - options	$ 45.79
Unrecognized future expense of RSUs	$ 286
Unrecognized future expense of stock options	$ 65
Term until expiration from grant date - options	8 years
Stock Options [Member]
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Service period over which grants vest	4 years
Weighted average period to expense unrecognized stock-based compensation expense	2 years 8 months 12 days
Restricted Stock Units (RSUs) [Member]
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Weighted average period to expense unrecognized stock-based compensation expense	2 years 8 months 12 days
Restricted Stock Units (RSUs) [Member] | Maximum [Member]
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Payout on stock-based compensation award (percent)	120.00%
Service period over which grants vest	4 years
Restricted Stock Units (RSUs) [Member] | Minimum [Member]
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Payout on stock-based compensation award (percent)	0.00%
Service period over which grants vest	1 year