Derivative and Other Hedging Instruments (US Treasury Securities) (Details) (USD $) In Millions, unless otherwise specified	Mar. 31, 2015	Dec. 31, 2014
Derivative [Line Items]
U.S. Treasury securities, net	$ 965	$ (2,936)
3 Year Maturity [Member] [Member]
Derivative [Line Items]
U.S. Treasury securities, net	(900)
5 Year Maturity [Member]
Derivative [Line Items]
U.S. Treasury securities, net	(2,111)
7 Years Maturity [Member]
Derivative [Line Items]
U.S. Treasury securities, net	(339)
10 Year Maturity [Member]
Derivative [Line Items]
U.S. Treasury securities, net	4,258
Fair Value Hedging [Member]
Derivative [Line Items]
U.S. Treasury securities, net	965	(2,936)
Fair Value Hedging [Member] | 3 Year Maturity [Member] [Member]
Derivative [Line Items]
U.S. Treasury securities, net	(902)
Fair Value Hedging [Member] | 5 Year Maturity [Member]
Derivative [Line Items]
U.S. Treasury securities, net	(2,116)	(4,645)
Fair Value Hedging [Member] | 7 Years Maturity [Member]
Derivative [Line Items]
U.S. Treasury securities, net	(341)	(718)
Fair Value Hedging [Member] | 10 Year Maturity [Member]
Derivative [Line Items]
U.S. Treasury securities, net	4,324	2,427
At Par Value [Member]
Derivative [Line Items]
U.S. Treasury securities, net	908	(2,981)
At Par Value [Member] | 5 Year Maturity [Member]
Derivative [Line Items]
U.S. Treasury securities, net		(4,674)
At Par Value [Member] | 7 Years Maturity [Member]
Derivative [Line Items]
U.S. Treasury securities, net		(717)
At Par Value [Member] | 10 Year Maturity [Member]
Derivative [Line Items]
U.S. Treasury securities, net		2,410
At Cost Basis [Member]
Derivative [Line Items]
U.S. Treasury securities, net	974	(2,945)
At Cost Basis [Member] | 3 Year Maturity [Member] [Member]
Derivative [Line Items]
U.S. Treasury securities, net	(899)
At Cost Basis [Member] | 5 Year Maturity [Member]
Derivative [Line Items]
U.S. Treasury securities, net	(2,096)	(4,650)
At Cost Basis [Member] | 7 Years Maturity [Member]
Derivative [Line Items]
U.S. Treasury securities, net	(334)	(717)
At Cost Basis [Member] | 10 Year Maturity [Member]
Derivative [Line Items]
U.S. Treasury securities, net	$ 4,303	$ 2,422