Fair Value Measurement and Fair Value of Financial Instruments (Details 5) - USD ($) $ in Millions		Sep. 30, 2015	Dec. 31, 2014
Assets
Fair value of securities held to maturity		$ 10,528	$ 8,412
Level 1
Assets
Cash and cash equivalents		4,374	5,751
Level 2
Assets
Fair value of securities held to maturity		10,528	8,412
Liabilities
Deposits		82,759	86,076
Commercial paper and other short-term borrowings		2,338	2,704
Long-term debt		11,393	7,073
Level 3
Assets
Loans held for investment, net of allowance for loan losses	[1]	76,858	77,324
Other assets		14	11
Off-Balance Sheet Instruments
Commitments to extend credit and standby and commercial letters of credit		220	269
Carrying Amount
Assets
Cash and cash equivalents		4,374	5,751
Fair value of securities held to maturity		10,341	8,291
Loans held for investment, net of allowance for loan losses	[1]	75,353	75,475
Other assets		16	59
Liabilities
Deposits		82,693	86,004
Commercial paper and other short-term borrowings		2,338	2,704
Long-term debt		11,357	6,972
Off-Balance Sheet Instruments
Commitments to extend credit and standby and commercial letters of credit		220	269
Fair Value
Assets
Cash and cash equivalents		4,374	5,751
Fair value of securities held to maturity		10,528	8,412
Loans held for investment, net of allowance for loan losses	[1]	76,858	77,324
Other assets		14	11
Liabilities
Deposits		82,759	86,076
Commercial paper and other short-term borrowings		2,338	2,704
Long-term debt		11,393	7,073
Off-Balance Sheet Instruments
Commitments to extend credit and standby and commercial letters of credit		$ 220	$ 269

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