Investment Securities (Narrative) (Details) - USD ($) $ in Millions	Mar. 31, 2016	Dec. 31, 2015
Schedule of Investments [Line Items]
Other Than Temporary Impairment Credit Losses Recognized In Earnings Credit Losses On Debt Securities Held	$ 1,100
Gross unrealized loss on debt securities held to maturity in a continuous loss position for less than 12 months - fair value	600	$ 5,500
Gross unrealized loss on debt securities held to maturity in a continuous loss position for less than 12 months	6	59
Gross unrealized loss on debt securities held to maturity in a continuous loss position greater than 12 months	13	23
Gross unrealized loss on debt securities held to maturity	19	82
Gain on derivatives used to hedge purchase of investment securities	100
Gross unrealized loss on debt securities held to maturity in a continuous loss position greater than 12 months - fair value	1,700	$ 953
Federal Home Loan Mortgage Corporation Certificates And Obligations [FHLMC Member]
Schedule of Investments [Line Items]
Fair value of debt securities of a single issuer that exceeeds 10 percent of shareholders equity	4,900
Amortized cost of debt securities of a single issuer that exceeeds 10 percent of shareholders equity	4,800
Federal National Mortgage Association Certificates And Obligations [FNMA Member]
Schedule of Investments [Line Items]
Fair value of debt securities of a single issuer that exceeeds 10 percent of shareholders equity	23,200
Amortized cost of debt securities of a single issuer that exceeeds 10 percent of shareholders equity	$ 22,800