Fair Value Measurement and Fair Value of Financial Instruments (Details 7) (USD $) In Millions, unless otherwise specified	Sep. 30, 2013	Dec. 31, 2012
Assets
Securities held to maturity	$ 5,450	$ 1,135
Level 1
Assets
Cash and cash equivalents	7,312	5,491
Level 2
Assets
Securities held to maturity	5,450	1,135
Liabilities
Deposits	79,618	74,524
Commercial paper and other short-term borrowings	3,078	1,363
Long-term debt	7,942	5,861
Level 3
Assets
Loans held for investment, net of allowance for loan losses	67,052	59,613
FDIC indemnification asset	108	151
Other assets	3	3
Off-Balance Sheet Instruments
Commitments to extend credit and standby and commercial letters of credit	267	262
Carrying Amount
Assets
Cash and cash equivalents	7,312	5,491
Securities held to maturity	5,446	1,103
Loans held for investment, net of allowance for loan losses	65,599	58,284
FDIC indemnification asset	191	338
Other assets	2	3
Liabilities
Deposits	79,415	74,304
Commercial paper and other short-term borrowings	3,078	1,363
Long-term debt	7,803	5,622
Off-Balance Sheet Instruments
Commitments to extend credit and standby and commercial letters of credit	267	262
Fair Value
Assets
Cash and cash equivalents	7,312	5,491
Securities held to maturity	5,450	1,135
Loans held for investment, net of allowance for loan losses	67,052	59,613
FDIC indemnification asset	108	151
Other assets	3	3
Liabilities
Deposits	79,618	74,524
Commercial paper and other short-term borrowings	3,078	1,363
Long-term debt	7,942	5,861
Off-Balance Sheet Instruments
Commitments to extend credit and standby and commercial letters of credit	$ 267	$ 262