Common and Preferred Shares and Warrants (Details Textuals) - USD ($)	12 Months Ended
	Dec. 31, 2018	Dec. 31, 2017	Dec. 31, 2016	Sep. 26, 2016
Common And Preferred Shares And Warrants (Textuals) [Abstract]
Common share repurchases authorized				150,000,000
Common shares repurchased	(15,000,000)	(50,000,000)	(70,000,000)
Common shares remaining under share repurchase authorizations	70,000,000
Shares held as treasury shares	2,700,000	2,900,000	3,000,000
Cost basis of treasury stock	$ 207,000,000	$ 217,000,000	$ 197,000,000
Preferred shares, authorized	20,000,000	20,000,000
Preferred shares, par value	$ 1.67	$ 1.67
Depositary Shares, Redemption Amount	$ 1,000
Warrants, issued and outstanding	0	0	0
Liquidation price per share	$ 1,000,000
Share Repurchase Commissions [Line Items]
Commissions paid included in cost basis of common stock repurchased	$ 2,200,000	$ 2,900,000	$ 1,200,000
Cost basis of common stock repurchased	$ 1,600,000,000	$ 4,300,000,000	$ 4,400,000,000