Stockholders' Equity - Narrative (Details) (USD $) Share data in Millions, unless otherwise specified	3 Months Ended		6 Months Ended
	Jun. 30, 2014	Jun. 30, 2013	Jun. 30, 2014	Jun. 30, 2013	Oct. 31, 2013	Jan. 31, 2013
Stockholders' Equity Note [Abstract]
Stock repurchase program, authorized amount					$ 750,000,000	$ 150,000,000
Shares repurchased during period (in shares)	1.3	1.1	3.3	2.2
Value of shares repurchased during period	71,300,000	42,500,000	187,500,000	82,800,000
Amortization expense from capitalized stock-based compensation	$ 2,000,000	$ 2,000,000	$ 3,900,000	$ 3,900,000