Consolidated Statement of Changes in Shareholders' Equity (USD $) In Millions, unless otherwise specified	3 Months Ended			12 Months Ended
	Dec. 31, 2012	Dec. 31, 2011	Mar. 31, 2011	Dec. 31, 2012	Dec. 31, 2011	Dec. 31, 2010
Convertible preferred stock - savings plan
Convertible preferred stock - savings plan, balance, beginning of year			$ 68		$ 68	$ 79
Convertible preferred stock - savings plan, redemptions					(5)	(11)
Convertible preferred stock - savings plan, conversion to common stock					(63)
Convertible preferred stock - savings plan, balance, end of year						68
Common stock
Common stock, balance, beginning of year			20,162	20,732	20,162	19,593
Common stock, employee share-based compensation				261	328	420
Common stock, common shares issued - conversion of preferred stock					93
Common stock, compensation amortization under share-based plans and other changes				168	149	149
Common stock, balance, end of year	21,161	20,732		21,161	20,732	20,162
Retained earnings
Retained earnings, balance, beginning of year			18,847	19,579	18,847	16,315
Net income	304	618	839	2,473	1,426	3,216
Dividends				(700)	(669)	(677)
Premium on preferred stock converted to common stock					(30)
Retained earnings, other					5	(7)
Retained earnings, balance, end of year	21,352	19,579		21,352	19,579	18,847
Accumulated other comprehensive income, net of tax
Accumulated other comprehensive income, net of tax, balance, beginning of year			1,255	2,005	1,255	1,219
Other comprehensive income				231	750	36
Accumulated other comprehensive income, net of tax, balance, end of year	2,236	2,005		2,236	2,005	1,255
Treasury stock (at cost)
Treasury stock (at cost), balance, beginning of year			(14,857)	(17,839)	(14,857)	(9,791)
Treasury stock (at cost), treasury stock acquired - share repurchase authorization				(1,450)	(2,900)	(5,000)
Treasury stock (at cost), net shares acquired related to employee share-based compensation plans				(55)	(82)	(66)
Treasury stock (at cost), balance, end of year	(19,344)	(17,839)		(19,344)	(17,839)	(14,857)
Total common shareholders' equity	25,405	24,477		25,405	24,477	25,407
Total shareholders' equity	$ 25,405	$ 24,477		$ 25,405	$ 24,477	$ 25,475
Common shares outstanding
Common shares outstanding, balance, beginning of year			434.6	392.8	434.6	520.3
Common shares outstanding, treasury stock acquired - share repurchase authorization				(22.4)	(51.0)	(95.7)
Common shares outstanding, net shares issued under employee share-based compensation plans				7.0	7.7	10.0
Common shares outstanding, common shares issued - conversion of preferred stock					1.5
Common shares outstanding, balance, end of year	377.4	392.8		377.4	392.8	434.6