Equity - Share Repurchase Program and Share Repurchase Activity (Details) - USD ($)	3 Months Ended		6 Months Ended
	Jun. 30, 2018	Jun. 30, 2017	Jun. 30, 2018	Jun. 30, 2017
Stockholders' Equity Note [Abstract]
Stock repurchase program, authorized amount	$ 1,200,000,000.0		$ 1,200,000,000.0
Stock repurchase program, remaining authorized repurchase amount	$ 1,000,000,000		$ 1,000,000,000
Number of shares repurchased (in shares)	524,435	101,614	763,703	320,366
Cash paid for repurchased shares (in thousands)	$ 67,877,000	$ 11,808,000	$ 96,271,000	$ 33,786,000
Treasury stock, average price paid per share (in dollars per share)	$ 131.23	$ 127.29	$ 116.20	$ 105.46