Long-Term Debt (Long-Term Debt Portfolio) (Details) (USD $) In Millions, unless otherwise specified	Mar. 31, 2013	Dec. 31, 2012
Debt Instrument [Line Items]
Long-term Debt, Current Maturities	$ 14,773	$ 12,573
Long-term Debt, Excluding Current Maturities	51,892	60,894
Derivative, Amount of Hedged Item	956	1,094
Long-term Debt	67,621	74,561
Unsecured Debt [Member]
Debt Instrument [Line Items]
Long-term Debt, Current Maturities	3,809	1,070
Long-term Debt, Excluding Current Maturities	28,448	31,486
Derivative, Amount of Hedged Item	956	1,094
Long-term Debt	33,213	33,650
Secured Debt [Member]
Debt Instrument [Line Items]
Long-term Debt, Current Maturities	10,964	11,503
Long-term Debt, Excluding Current Maturities	23,444	29,408
Derivative, Amount of Hedged Item	0	0
Long-term Debt	34,408	40,911
Trust Preferred Securities Subject to Mandatory Redemption [Member]
Debt Instrument [Line Items]
Long-term Debt, Excluding Current Maturities	$ 2,600	$ 2,600