Common and Preferred Shares and Warrants (Details Textuals) - USD ($)	12 Months Ended
	Dec. 31, 2017	Dec. 31, 2016	Dec. 31, 2015	Sep. 26, 2016
Share Repurchase [Domain]
Share Repurchase Commissions [Line Items]
Cost basis of common stock repurchased	$ 4,400,000,000	$ 4,498,000,000	$ 4,575,000,000
Common share repurchases authorized				150,000,000
Common shares repurchased	(50,000,000)	(70,000,000)	(58,800,000)
Common shares remaining under share repurchase authorizations	85,000,000
Shares held as treasury shares	2,900,000	3,000,000	3,000,000
Cost basis of treasury stock	$ 217,000,000	$ 197,000,000	$ 242,000,000
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
Commissions paid included in cost basis of common stock repurchased	$ 2,900,000	$ 1,200,000	$ 1,100,000
Cost basis of common stock repurchased	$ 4,300,000,000	$ 4,400,000,000	$ 4,500,000,000