Capital Structure (Details) (USD $)	0 Months Ended	3 Months Ended	6 Months Ended		0 Months Ended	6 Months Ended
	Jun. 20, 2013	Jun. 30, 2013	Jun. 30, 2013	Dec. 31, 2012	Jun. 12, 2013 5.625% Noncumulative Perpetual Preferred Stock	Jun. 30, 2013 5.625% Noncumulative Perpetual Preferred Stock	Jun. 30, 2013 5.625% Noncumulative Perpetual Preferred Stock Maximum item	Jun. 30, 2013 Commercial Paper	Dec. 31, 2012 7.50% Debentures, due 2013	Jun. 30, 2013 5.00% Senior Notes, due 2014	Dec. 31, 2012 5.00% Senior Notes, due 2014	Jun. 30, 2013 6.20% Senior Notes, due 2014	Dec. 31, 2012 6.20% Senior Notes, due 2014	Jun. 30, 2013 6.75% Senior Debentures, due 2018	Dec. 31, 2012 6.75% Senior Debentures, due 2018	Jun. 30, 2013 7.45% Senior Notes, due 2019	Dec. 31, 2012 7.45% Senior Notes, due 2019	Jun. 30, 2013 3.15% Senior Notes, due 2023	Jun. 07, 2013 3.15% Senior Notes, due 2023	Jun. 30, 2013 6.125% Senior Notes, due 2032	Dec. 31, 2012 6.125% Senior Notes, due 2032	Jun. 30, 2013 5.350% Senior Notes due 2033	Dec. 31, 2012 5.350% Senior Notes due 2033	Jun. 30, 2013 5.55% Senior Notes due 2035	Dec. 31, 2012 5.55% Senior Notes due 2035	Jun. 30, 2013 5.95% Senior Notes, due 2036	Dec. 31, 2012 5.95% Senior Notes, due 2036	Jun. 30, 2013 6.90% Senior Debentures, due 2038	Dec. 31, 2012 6.90% Senior Debentures, due 2038	Jun. 30, 2013 5.20% Senior Notes due 2042	Dec. 31, 2012 5.20% Senior Notes due 2042	Jun. 30, 2013 4.50% Senior Notes, due 2043	Jun. 07, 2013 4.50% Senior Notes, due 2043	Jun. 30, 2013 5.10% Subordinated Debentures, due 2053	Jan. 10, 2013 5.10% Subordinated Debentures, due 2053	Jun. 30, 2013 6.125% Junior Subordinated Debentures, due 2067	Dec. 31, 2012 6.125% Junior Subordinated Debentures, due 2067	Jun. 30, 2013 6.50% Junior Subordinated Debentures, due 2067	Dec. 31, 2012 6.50% Junior Subordinated Debentures, due 2067	Jun. 30, 2013 Synthetic lease VIE obligations, floating rates, due 2014	Dec. 31, 2012 Synthetic lease VIE obligations, floating rates, due 2014	Jun. 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																			$ 500,000,000														$ 500,000,000		$ 500,000,000
Repurchased principal amounts of debt	1,830,000,000
Loss on extinguishment of debt	(480,000,000)	(480,000,000)	(480,000,000)
Weighted average interest rate of short-term debt (as a percent)								0.32%
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%	6.125%	6.125%	6.50%	6.50%
Total long-term debt		5,475,000,000	5,475,000,000	6,057,000,000					250,000,000	650,000,000	650,000,000	300,000,000	300,000,000	177,000,000	250,000,000	325,000,000	700,000,000	500,000,000		160,000,000	250,000,000	323,000,000	400,000,000	563,000,000	800,000,000	405,000,000	650,000,000	165,000,000	250,000,000	88,000,000	500,000,000	500,000,000		500,000,000		263,000,000	500,000,000	500,000,000	500,000,000	44,000,000	44,000,000	12,000,000	13,000,000
Short-term debt		500,000,000	500,000,000					500,000,000
Total debt		5,975,000,000	5,975,000,000	6,057,000,000
Redemption price as percentage of principal amount plus accrued and unpaid interest			100.00%
Preferred stock
Preferred stock, issued shares		11,500	11,500	0	11,500
Preferred stock stated dividend rate (as a percent)					5.625%	5.625%
Preferred stock, par value (in dollars per share)		$ 1	$ 1	$ 1	$ 1.00
Preferred stock, shares liquidation preference (in dollars per share)					$ 25,000
Aggregate proceeds from issue of preferred stock					$ 287,500,000
Additional members of the board of directors							2
Preferred stock, redemption price (in dollars per share)					$ 25,000	$ 25,000