Stockholders' Equity (Details) - USD ($) $ in Millions	3 Months Ended							12 Months Ended
	Dec. 31, 2015	Sep. 30, 2015	Jun. 30, 2015	Mar. 31, 2015	Dec. 31, 2014	Jun. 30, 2014	Mar. 31, 2014	Dec. 31, 2015	Dec. 31, 2014	Dec. 31, 2013
Stock Repurchase Program [Roll Forward]
Purchase of treasury stock (in dollars)								$ 527.0	$ 1,924.0
Ending balance of treasury stock (in dollars)	$ 153.0							$ 153.0
The 2012 Share Repurchase Program
Stock Repurchase Program [Roll Forward]
Beginning balance of accumulated number of shares repurchased (in shares)				68,100,000				68,100,000
Number of shares repurchased (in shares)						15,400,000	16,000,000		31,400,000	36,700,000
Ending balance of accumulated number of shares repurchased (in shares)					68,100,000				68,100,000
Beginning balance of treasury stock (in dollars)				$ 3,000.0				$ 3,000.0
Purchase of treasury stock (in dollars)						$ 757.0	$ 794.0		$ 1,551.0	$ 1,449.0
Ending balance of treasury stock (in dollars)					$ 3,000.0				$ 3,000.0
The 2014 Share Repurchase Program
Stock Repurchase Program [Roll Forward]
Beginning balance of accumulated number of shares repurchased (in shares)				7,000,000				7,000,000
Number of shares repurchased (in shares)	0	300,000	4,500,000	4,100,000	7,000,000			8,900,000	7,000,000
Ending balance of accumulated number of shares repurchased (in shares)	15,900,000.0				7,000,000			15,900,000.0	7,000,000
Beginning balance of treasury stock (in dollars)				$ 373.0				$ 373.0
Purchase of treasury stock (in dollars)	$ 0.0	$ 22.0	$ 268.0	$ 237.0	$ 373.0			527.0	$ 373.0
Ending balance of treasury stock (in dollars)	$ 900.0				$ 373.0			$ 900.0	$ 373.0