Common and Preferred Shares and Warrants (Details) - shares shares in Millions	12 Months Ended
	Dec. 31, 2015	Dec. 31, 2014	Dec. 31, 2013
Authorized shares and a reconciliation of common shares issued and outstanding
Common shares, authorized	3,600	3,600	3,600
Shares issued and outstanding at beginning of year	1,023	1,064	1,105
Repurchases of common shares	(59)	(49)	(55)
Other, primarily stock option exercises and RSAs granted	5	8	14
Shares issued and outstanding as of December 31	969	1,023	1,064
Stockholders' Equity Note (Textuals) [Abstract]
Shares reserved for issuance under employee stock and employee benefit plans	51