Common and Preferred Shares (Details Textuals) - USD ($)	12 Months Ended
	Dec. 31, 2019	Dec. 31, 2018	Dec. 31, 2017	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)	40,000,000	15,000,000	50,000,000
Common shares remaining under share repurchase authorizations (in shares)	109,000,000
Shares held as treasury shares (in shares)	2,600,000	2,700,000	2,900,000
Cost basis of treasury stock	$ 292,000,000	$ 207,000,000	$ 217,000,000
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	$ 4,600,000,000	$ 1,600,000,000	$ 4,300,000,000
Commissions paid included in cost basis of common stock repurchased	$ 6,200,000	$ 2,200,000	$ 2,900,000