Shareholders' Equity Shareholders' Equity (Narrative) (Details) - USD ($) $ / shares in Units, $ in Millions	12 Months Ended
	Dec. 31, 2019	Dec. 31, 2018	Dec. 31, 2017
Stock Option
Common stock shares reserved for future issuance	3,800,000
Restricted Stock
Shares of non-vested restricted stock outstanding	458,000	869,000
Common Stock
Shares repurchased under equity repurchase program	(18,700,000)	(14,900,000)	(7,500,000)
Warrants
Year of expiration for outstanding warrants	2018
Shares of common stock issued upon exercise of warrants		585,000	1,800,000
Equity Repurchase Program | Common Stock
Shares repurchased under equity repurchase program	18,600,000		7,300,000
Average cost per share of shares repurchased under equity repurchase program	$ 73.60	$ 89.21	$ 72.44
Stock repurchased during the period	$ 1,400