Fair Value Measurement and Fair Value of Financial Instruments (Details 5) - USD ($) $ in Millions		Mar. 31, 2016	Dec. 31, 2015
Assets
Fair value of securities held to maturity		$ 10,848	$ 10,207
Level 1
Assets
Cash and cash equivalents		8,324	4,529
Level 2
Assets
Fair value of securities held to maturity		10,848	10,207
Liabilities
Deposits		89,548	84,375
Commercial paper and other short-term borrowings		647	1,038
Long-term debt		11,900	12,351
Level 3
Assets
Loans held for investment, net of allowance for loan losses	[1]	79,411	77,640
Other assets			17
Off-Balance Sheet Instruments
Commitments to extend credit and standby and commercial letters of credit		241	243
Carrying Amount
Assets
Cash and cash equivalents		8,324	4,529
Fair value of securities held to maturity		10,605	10,158
Loans held for investment, net of allowance for loan losses	[1]	77,697	76,150
Other assets			16
Liabilities
Deposits		89,500	84,340
Commercial paper and other short-term borrowings		647	1,038
Long-term debt		11,843	12,349
Off-Balance Sheet Instruments
Commitments to extend credit and standby and commercial letters of credit		241	243
Fair Value
Assets
Cash and cash equivalents		8,324	4,529
Fair value of securities held to maturity		10,848	10,207
Loans held for investment, net of allowance for loan losses	[1]	79,411	77,640
Other assets			17
Liabilities
Deposits		89,548	84,375
Commercial paper and other short-term borrowings		647	1,038
Long-term debt		11,900	12,351
Off-Balance Sheet Instruments
Commitments to extend credit and standby and commercial letters of credit		$ 241	$ 243

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