Long-Term Debt (Details) (USD $)	12 Months Ended
	Dec. 31, 2012		Dec. 31, 2011
Debt Instrument [Line Items]
Long-term debt instruments	$ 6,086,000,000		$ 4,101,000,000
Debt due within one year	(20,000,000)		(17,000,000)
Reclassified from short-term debt	5,900,000,000		5,600,000,000
Total long-term debt	11,966,000,000		9,684,000,000
Long-term debt maturing 2013	20,000,000
Long-term debt maturing 2014	23,000,000
Long-term debt maturing 2015	0
Long-term debt maturing 2016	0
Long-term debt maturing 2017	2,000,000,000
Long-term debt maturing after 2017	4,043,000,000
3.95% notes due 2014 [Member]
Debt Instrument [Line Items]
Interest rate	3.95%
Total bonds redeemed in 2012	2,000,000,000
Notes Payable [Member] | 3.95% notes due 2014 [Member]
Debt Instrument [Line Items]
Long-term debt instruments	0		1,998,000,000
Interest rate	3.95%
Notes Payable [Member] | 1.104% notes due 2017 [Member]
Debt Instrument [Line Items]
Long-term debt instruments	2,000,000,000		0
Interest rate	1.104%
Notes Payable [Member] | 2.356% notes due 2022 [Member]
Debt Instrument [Line Items]
Long-term debt instruments	2,000,000,000		0
Interest rate	2.356%
Notes Payable [Member] | 4.95% notes due 2019 [Member]
Debt Instrument [Line Items]
Long-term debt instruments	1,500,000,000		1,500,000,000
Interest rate	4.95%
Notes Payable [Member] | 7.327% amortizing notes due 2014 [Member]
Debt Instrument [Line Items]
Long-term debt instruments	43,000,000	[1]	59,000,000	[1]
Interest rate	7.327%
Debentures [Member] | 8.625% debentures due 2032 [Member]
Debt Instrument [Line Items]
Long-term debt instruments	147,000,000		147,000,000
Interest rate	8.625%
Debentures [Member] | 8.625 % debentures due 2031 [Member]
Debt Instrument [Line Items]
Long-term debt instruments	107,000,000		107,000,000
Interest rate	8.625%
Debentures [Member] | 7.5 % debentures due 2043 [Member]
Debt Instrument [Line Items]
Long-term debt instruments	83,000,000		83,000,000
Interest rate	7.50%
Debentures [Member] | 8 % debentures due 2032 [Member]
Debt Instrument [Line Items]
Long-term debt instruments	74,000,000		74,000,000
Interest rate	8.00%
Debentures [Member] | 9.75 % debentures due 2020 [Member]
Debt Instrument [Line Items]
Long-term debt instruments	54,000,000		54,000,000
Interest rate	9.75%
Debentures [Member] | 8.875 % debentures due 2021 [Member]
Debt Instrument [Line Items]
Long-term debt instruments	40,000,000		40,000,000
Interest rate	8.875%
Medium-term Notes [Member] | Medium-term notes, maturing from 2021 to 2038 (5.92%) [Member]
Debt Instrument [Line Items]
Long-term debt instruments	38,000,000	[2]	38,000,000	[2]
Interest rate	5.92%
Other Long Term Debt [Member] | Other long-term debt (8.07%) [Member]
Debt Instrument [Line Items]
Long-term debt instruments	0	[2]	1,000,000	[2]
Interest rate	8.07%
Corporate Bond Securities [Member]
Debt Instrument [Line Items]
Debt issued	$ 4,000,000,000

[1] Guarantee of ESOP debt.

[2] Weighted-average interest rate at December 31, 2012 and 2011.