Common and Preferred Shares (Details Textuals) - USD ($) $ / shares in Units, $ in Millions	12 Months Ended
	Dec. 31, 2020	Dec. 31, 2019	Dec. 31, 2018	Sep. 23, 2019
Common And Preferred Shares And Warrants (Textuals) [Abstract]
Common share repurchases authorized (up to) (in shares)				120,000,000
Common shares repurchased (in shares)	7,000,000	40,000,000	15,000,000
Common shares remaining under share repurchase authorizations (in shares)	102,000,000
Shares held as treasury shares (in shares)	2,500,000	2,600,000	2,700,000
Cost basis of treasury stock	$ 279.0	$ 292.0	$ 207.0
Preferred shares, authorized (in shares)	20,000,000	20,000,000
Preferred shares, par value (in dollars per share)	$ 1.667	$ 1.667
Liquidation price per share (in dollars per share)	1,000,000
Depositary shares redemption amount	$ 1,000
Warrants, issued and outstanding (in shares)	0	0	0
Repurchase Agreements [Member]
Share Repurchase Commissions [Line Items]
Cost basis of common stock repurchased	$ 900.0	$ 4,600.0	$ 1,600.0
Commissions paid included in cost basis of common stock repurchased	$ 1.0	$ 6.2	$ 2.2