Equity - Share Repurchase Program and Share Repurchase Activity (Details) - USD ($)	3 Months Ended		9 Months Ended
	Sep. 30, 2018	Sep. 30, 2017	Sep. 30, 2018	Sep. 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)	51,298	26,725	815,001	348,236
Cash paid for repurchased shares (in thousands)	$ 8,129,000	$ 3,275,000	$ 104,400,000	$ 37,188,000
Treasury stock, average price paid per share (in dollars per share)	$ 140.09	$ 128.10	$ 122.53	$ 106.79