Capital Structure (Details) (USD $) In Millions, except Share data, unless otherwise specified	0 Months Ended	3 Months Ended	9 Months Ended						0 Months Ended
	Jun. 20, 2013	Sep. 30, 2013	Sep. 30, 2013	Aug. 08, 2013	Dec. 31, 2012	Sep. 30, 2013 Noncumulative Perpetual Preferred Stock	Jun. 12, 2013 Noncumulative Perpetual Preferred Stock	Sep. 30, 2013 Noncumulative Perpetual Preferred Stock Maximum item	Jun. 12, 2013 Noncumulative Perpetual Preferred Stock, Series A	Sep. 30, 2013 Noncumulative Perpetual Preferred Stock, Series C	Dec. 31, 2012 7.50% Debentures, due 2013	Sep. 30, 2013 5.00% Senior Notes, due 2014	Dec. 31, 2012 5.00% Senior Notes, due 2014	Sep. 30, 2013 6.20% Senior Notes, due 2014	Dec. 31, 2012 6.20% Senior Notes, due 2014	Sep. 30, 2013 6.75% Senior Debentures, due 2018	Dec. 31, 2012 6.75% Senior Debentures, due 2018	Sep. 30, 2013 7.45% Senior Notes, due 2019	Dec. 31, 2012 7.45% Senior Notes, due 2019	Sep. 30, 2013 3.15% Senior Notes, due 2023	Jun. 07, 2013 3.15% Senior Notes, due 2023	Sep. 30, 2013 6.125% Senior Notes, due 2032	Dec. 31, 2012 6.125% Senior Notes, due 2032	Sep. 30, 2013 5.350% Senior Notes due 2033	Dec. 31, 2012 5.350% Senior Notes due 2033	Sep. 30, 2013 5.55% Senior Notes due 2035	Dec. 31, 2012 5.55% Senior Notes due 2035	Sep. 30, 2013 5.95% Senior Notes, due 2036	Dec. 31, 2012 5.95% Senior Notes, due 2036	Sep. 30, 2013 6.90% Senior Debentures, due 2038	Dec. 31, 2012 6.90% Senior Debentures, due 2038	Sep. 30, 2013 5.20% Senior Notes due 2042	Dec. 31, 2012 5.20% Senior Notes due 2042	Sep. 30, 2013 4.50% Senior Notes, due 2043	Jun. 07, 2013 4.50% Senior Notes, due 2043	Sep. 30, 2013 5.10% Subordinated Debentures, due 2053	Jan. 10, 2013 5.10% Subordinated Debentures, due 2053	Sep. 30, 2013 5.75% Subordinated Debentures, due 2053	Aug. 08, 2013 5.75% Subordinated Debentures, due 2053	Sep. 30, 2013 6.125% Junior Subordinated Debentures, due 2067	Dec. 31, 2012 6.125% Junior Subordinated Debentures, due 2067	Sep. 30, 2013 6.50% Junior Subordinated Debentures, due 2067	Dec. 31, 2012 6.50% Junior Subordinated Debentures, due 2067	Sep. 30, 2013 Synthetic lease VIE obligations, floating rates, due 2014	Dec. 31, 2012 Synthetic lease VIE obligations, floating rates, due 2014	Sep. 30, 2013 Federal Home Loan Bank ("FHLB") advances, due 2018	Dec. 31, 2012 Federal Home Loan Bank ("FHLB") advances, due 2018
Debt outstanding:
Face amount of debt issued																					$ 500														$ 500		$ 500		$ 800
Repurchased principal amounts of debt	1,830	57	57	57
Loss on extinguishment of debt	(480)	(9)	(489)
Note stated interest rate (as a percent)											7.50%	5.00%	5.00%	6.20%	6.20%	6.75%	6.75%	7.45%	7.45%	3.15%	3.15%	6.125%	6.125%	5.35%	5.35%	5.55%	5.55%	5.95%	5.95%	6.90%	6.90%	5.20%	5.20%	4.50%	4.50%	5.10%	5.10%	5.75%	5.75%	6.125%	6.125%	6.50%	6.50%
Total long-term debt		6,217	6,217		6,057						250	650	650	300	300	176	250	317	700	500		159	250	323	400	555	800	386	650	165	250	72	500	500		500		800		259	500	500	500	44	44	11	13
Total debt		6,217	6,217		6,057
Redemption price as percentage of principal amount plus accrued and unpaid interest			100.00%
Preferred stock
Preferred stock, issued shares		26,900	26,900		0				11,500	15,400
Preferred stock stated dividend rate (as a percent)									5.625%	6.75%
Preferred stock, par value (in dollars per share)		$ 1	$ 1		$ 1				$ 1.00	$ 1.00
Preferred stock, shares liquidation preference (in dollars per share)									$ 25,000	$ 25,000
Gross proceeds from issue of preferred stock									$ 287.5	$ 385.0
Additional members of the board of directors								2
Preferred stock, redemption price (in dollars per share)						$ 25,000	$ 25,000