Treasury Stock (Details) - USD ($)	1 Months Ended		3 Months Ended		9 Months Ended
	Apr. 30, 2018	Feb. 28, 2018	Sep. 30, 2019	Sep. 30, 2018	Sep. 30, 2019	Sep. 30, 2018	Oct. 31, 2019	Oct. 31, 2018
Equity, Class of Treasury Stock [Line Items]
Stock repurchase program, authorized amount								$ 750,000,000.0
Document Period End Date					Sep. 30, 2019
Available to repurchase common stock			$ 414,000,000.0		$ 414,000,000.0
Amount expended on share repurchases in open market transactions			$ 103,905,000	$ 116,175,000	$ 353,904,000	$ 881,154,000
Number of shares withheld to satisfy minimum tax withholding obligations			44,829	32,813	742,946	570,589
Payment for tax withholding related to vested stock units			$ 4,200,000	$ 3,700,000	$ 74,800,000	$ 53,600,000
Open Market Purchases [Member]
Equity, Class of Treasury Stock [Line Items]
Amount expended on share repurchases in open market transactions			$ 103,900,000	$ 116,200,000	$ 353,900,000	$ 131,200,000
Stock repurchases net (shares)			1,130,100	1,000,000.0	3,640,982	1,200,000
Average per share price on share repurchases in open market transactions (in dollars per share)			$ 91.94	$ 111.11	$ 97.20	$ 110.60
ASR Counterparty [Member]
Equity, Class of Treasury Stock [Line Items]
Amount expended on share repurchases in open market transactions		$ 750,000,000.0
Stock repurchases net (shares)	1,600,000	6,500,000
Subsequent Event [Member]
Equity, Class of Treasury Stock [Line Items]
Stock repurchase program, authorized amount							$ 600,000,000.0