Shareholders' Equity (Details) - USD ($)	1 Months Ended					3 Months Ended						6 Months Ended		12 Months Ended
	Jul. 31, 2019	Apr. 30, 2019	Jul. 31, 2018	May 31, 2018	Apr. 30, 2018	Jun. 30, 2019	Mar. 31, 2019	Dec. 31, 2018	Jun. 30, 2018	Mar. 31, 2018	Dec. 31, 2017	Jun. 30, 2019	Jun. 30, 2018	Dec. 31, 2018
Subsequent Event [Line Items]
Dividend declared (in dollars per share)						$ 0.7	$ 0.70	$ 0.70	$ 0.6	$ 0.60	$ 0.60	$ 1.40	$ 1.20
Common stock, dividends, per share, cash paid (in dollars per share)		$ 0.70	$ 0.60		$ 0.60		$ 0.70			$ 0.60
Length of repurchase program				24 months
Common stock repurchase program, authorized amount				$ 1,000,000,000.0
Treasury stock, shares, acquired (in shares)						0						0		2,800,000
Treasury stock, value, acquired, cost method									$ 137,460,000				$ 412,499,000	$ 300,000,000.0
Remaining authorized repurchase amount						$ 700,000,000.0						$ 700,000,000.0
Forecast | Subsequent Event
Subsequent Event [Line Items]
Common stock, dividends, per share, cash paid (in dollars per share)	$ 0.70