Fair Value, Measurements From Brokers or Third Party Pricing Services (Details) - USD ($) $ in Millions	Jun. 30, 2015	Dec. 31, 2014
Financial assets
Available-for-sale, at fair value	$ 260,667	$ 257,442
Derivatives (trading and other assets)	83,895	88,474
Financial liabilities
Derivatives (liabilities)	(81,075)	(83,781)
Brokers [Member] | Fair Value, Inputs, Level 1 [Member]
Financial assets
Trading assets (excluding derivatives)	0	0
Available-for-sale, at fair value	0	0
Derivatives (trading and other assets)	0	0
Financial liabilities
Derivatives (liabilities)	0	0
Other liabilities	0	0
Brokers [Member] | Fair Value, Inputs, Level 1 [Member] | Debt Securities [Member]
Financial assets
Available-for-sale, at fair value	0	0
Brokers [Member] | Fair Value, Inputs, Level 1 [Member] | Securities of U.S. Treasury and federal agencies [Member]
Financial assets
Available-for-sale, at fair value	0	0
Brokers [Member] | Fair Value, Inputs, Level 1 [Member] | Securities of U.S. states and political subdivisions [Member]
Financial assets
Available-for-sale, at fair value	0	0
Brokers [Member] | Fair Value, Inputs, Level 1 [Member] | Mortgage-Backed Securities [Member]
Financial assets
Available-for-sale, at fair value	0	0
Brokers [Member] | Fair Value, Inputs, Level 1 [Member] | Other debt securities
Financial assets
Available-for-sale, at fair value	0	0
Brokers [Member] | Fair Value, Inputs, Level 1 [Member] | Equity Securities [Member]
Financial assets
Available-for-sale, at fair value	0	0
Brokers [Member] | Fair Value, Inputs, Level 2 [Member]
Financial assets
Trading assets (excluding derivatives)	0	0
Available-for-sale, at fair value	775	1,187
Derivatives (trading and other assets)	0	1
Financial liabilities
Derivatives (liabilities)	0	(1)
Other liabilities	0	0
Brokers [Member] | Fair Value, Inputs, Level 2 [Member] | Debt Securities [Member]
Financial assets
Available-for-sale, at fair value	775	1,187
Brokers [Member] | Fair Value, Inputs, Level 2 [Member] | Securities of U.S. Treasury and federal agencies [Member]
Financial assets
Available-for-sale, at fair value	0	0
Brokers [Member] | Fair Value, Inputs, Level 2 [Member] | Securities of U.S. states and political subdivisions [Member]
Financial assets
Available-for-sale, at fair value	31	0
Brokers [Member] | Fair Value, Inputs, Level 2 [Member] | Mortgage-Backed Securities [Member]
Financial assets
Available-for-sale, at fair value	183	152
Brokers [Member] | Fair Value, Inputs, Level 2 [Member] | Other debt securities
Financial assets
Available-for-sale, at fair value	561	1,035
Brokers [Member] | Fair Value, Inputs, Level 2 [Member] | Equity Securities [Member]
Financial assets
Available-for-sale, at fair value	0	0
Brokers [Member] | Fair Value, Inputs, Level 3 [Member]
Financial assets
Trading assets (excluding derivatives)	0	0
Available-for-sale, at fair value	554	601
Derivatives (trading and other assets)	0	0
Financial liabilities
Derivatives (liabilities)	0	0
Other liabilities	0	0
Brokers [Member] | Fair Value, Inputs, Level 3 [Member] | Debt Securities [Member]
Financial assets
Available-for-sale, at fair value	554	601
Brokers [Member] | Fair Value, Inputs, Level 3 [Member] | Securities of U.S. Treasury and federal agencies [Member]
Financial assets
Available-for-sale, at fair value	0	0
Brokers [Member] | Fair Value, Inputs, Level 3 [Member] | Securities of U.S. states and political subdivisions [Member]
Financial assets
Available-for-sale, at fair value	0	0
Brokers [Member] | Fair Value, Inputs, Level 3 [Member] | Mortgage-Backed Securities [Member]
Financial assets
Available-for-sale, at fair value	0	0
Brokers [Member] | Fair Value, Inputs, Level 3 [Member] | Other debt securities
Financial assets
Available-for-sale, at fair value	554	601
Brokers [Member] | Fair Value, Inputs, Level 3 [Member] | Equity Securities [Member]
Financial assets
Available-for-sale, at fair value	0	0
Third party pricing services [Member] | Fair Value, Inputs, Level 1 [Member]
Financial assets
Trading assets (excluding derivatives)	3	2
Available-for-sale, at fair value	29,989	19,899
Derivatives (trading and other assets)	0	0
Financial liabilities
Derivatives (liabilities)	0	0
Other liabilities	0	0
Third party pricing services [Member] | Fair Value, Inputs, Level 1 [Member] | Debt Securities [Member]
Financial assets
Available-for-sale, at fair value	29,989	19,899
Third party pricing services [Member] | Fair Value, Inputs, Level 1 [Member] | Securities of U.S. Treasury and federal agencies [Member]
Financial assets
Available-for-sale, at fair value	29,989	19,899
Third party pricing services [Member] | Fair Value, Inputs, Level 1 [Member] | Securities of U.S. states and political subdivisions [Member]
Financial assets
Available-for-sale, at fair value	0	0
Third party pricing services [Member] | Fair Value, Inputs, Level 1 [Member] | Mortgage-Backed Securities [Member]
Financial assets
Available-for-sale, at fair value	0	0
Third party pricing services [Member] | Fair Value, Inputs, Level 1 [Member] | Other debt securities
Financial assets
Available-for-sale, at fair value	0	0
Third party pricing services [Member] | Fair Value, Inputs, Level 1 [Member] | Equity Securities [Member]
Financial assets
Available-for-sale, at fair value	0	0
Third party pricing services [Member] | Fair Value, Inputs, Level 2 [Member]
Financial assets
Trading assets (excluding derivatives)	54	105
Available-for-sale, at fair value	221,896	227,070
Derivatives (trading and other assets)	253	290
Financial liabilities
Derivatives (liabilities)	(249)	(292)
Other liabilities	0	(1)
Third party pricing services [Member] | Fair Value, Inputs, Level 2 [Member] | Debt Securities [Member]
Financial assets
Available-for-sale, at fair value	221,395	226,501
Third party pricing services [Member] | Fair Value, Inputs, Level 2 [Member] | Securities of U.S. Treasury and federal agencies [Member]
Financial assets
Available-for-sale, at fair value	5,955	5,905
Third party pricing services [Member] | Fair Value, Inputs, Level 2 [Member] | Securities of U.S. states and political subdivisions [Member]
Financial assets
Available-for-sale, at fair value	46,333	42,666
Third party pricing services [Member] | Fair Value, Inputs, Level 2 [Member] | Mortgage-Backed Securities [Member]
Financial assets
Available-for-sale, at fair value	123,562	135,997
Third party pricing services [Member] | Fair Value, Inputs, Level 2 [Member] | Other debt securities
Financial assets
Available-for-sale, at fair value	45,545	41,933
Third party pricing services [Member] | Fair Value, Inputs, Level 2 [Member] | Equity Securities [Member]
Financial assets
Available-for-sale, at fair value	501	569
Third party pricing services [Member] | Fair Value, Inputs, Level 3 [Member]
Financial assets
Trading assets (excluding derivatives)	0	0
Available-for-sale, at fair value	624	735
Derivatives (trading and other assets)	0	0
Financial liabilities
Derivatives (liabilities)	0	0
Other liabilities	0	0
Third party pricing services [Member] | Fair Value, Inputs, Level 3 [Member] | Debt Securities [Member]
Financial assets
Available-for-sale, at fair value	624	735
Third party pricing services [Member] | Fair Value, Inputs, Level 3 [Member] | Securities of U.S. Treasury and federal agencies [Member]
Financial assets
Available-for-sale, at fair value	0	0
Third party pricing services [Member] | Fair Value, Inputs, Level 3 [Member] | Securities of U.S. states and political subdivisions [Member]
Financial assets
Available-for-sale, at fair value	53	61
Third party pricing services [Member] | Fair Value, Inputs, Level 3 [Member] | Mortgage-Backed Securities [Member]
Financial assets
Available-for-sale, at fair value	103	133
Third party pricing services [Member] | Fair Value, Inputs, Level 3 [Member] | Other debt securities
Financial assets
Available-for-sale, at fair value	468	541
Third party pricing services [Member] | Fair Value, Inputs, Level 3 [Member] | Equity Securities [Member]
Financial assets
Available-for-sale, at fair value	$ 0	$ 0