Stock Repurchases (Details) - USD ($) shares in Millions			1 Months Ended	3 Months Ended		9 Months Ended
	Aug. 01, 2016	Feb. 10, 2016	Jul. 18, 2016	Sep. 30, 2016	Sep. 30, 2015	Sep. 30, 2016	Sep. 30, 2015
Stockholders' Equity Note [Abstract]
Stock repurchase program, authorized amount				$ 1,400,000,000		$ 1,400,000,000
Stock repurchase program, remaining authorized amount				96,200,000		$ 96,200,000
Accelerated share repurchases, initial price to be paid	$ 100,000,000	$ 200,000,000
Subsequent Event [Line Items]
Accelerated share repurchases, number of shares	0.5	1.3	0.2
Accelerated share repurchases, percentage of shares to be repurchased	75.00%	75.00%
Shares repurchased from employees who surrendered shares to satisfy minimum tax withholding obligations						0.2
Shares repurchased from employees who surrendered shares to satisfy minimum tax withholding obligations, value				$ 26,300,000	$ 23,500,000	$ 26,300,000	$ 23,500,000