Stockholders' Equity (Narrative) (Details)	6 Months Ended
	Jun. 30, 2020 USD ($)	Jun. 30, 2019 USD ($)	Dec. 31, 2019 shares	Nov. 27, 2019 £ / shares shares	Dec. 11, 2018 USD ($)	Apr. 25, 2017 USD ($)
Stockholders' Equity Note [Abstract]
Canceled shares (in shares) | shares			4,000,000.0
Shares Issued, Price Per Share | £ / shares				£ 1
Stock repurchase program, authorized amount	$ 800,000,000.0				$ 300,000,000.0	$ 500,000,000.0
Payments of Dividends	59,200,000	$ 116,600,000
Dividends, Common Stock, Cash	$ 59,200,000	$ 116,600,000
Shares Redeemed | shares				50,000