Fair Value Measurement and Fair Value of Financial Instruments (Details 5) - USD ($) $ in Millions		Jun. 30, 2015	Dec. 31, 2014	Dec. 31, 2013
Assets
Fair value of securities held to maturity		$ 10,103	$ 8,412	$ 8,412
Level 1
Assets
Cash and cash equivalents		4,043	5,751
Level 2
Assets
Fair value of securities held to maturity		10,103	8,412
Liabilities
Deposits		81,766	86,076
Commercial paper and other short-term borrowings		5,262	2,704
Long-term debt		8,887	7,073
Level 3
Assets
Loans held for investment, net of allowance for loan losses	[1]	76,783	77,324
Other assets		11	11
Off-Balance Sheet Instruments
Commitments to extend credit and standby and commercial letters of credit		257	269
Carrying Amount
Assets
Cash and cash equivalents		4,043	5,751
Fair value of securities held to maturity		10,002	8,291
Loans held for investment, net of allowance for loan losses	[1]	75,112	75,475
Other assets		16	59
Liabilities
Deposits		81,702	86,004
Commercial paper and other short-term borrowings		5,262	2,704
Long-term debt		8,852	6,972
Off-Balance Sheet Instruments
Commitments to extend credit and standby and commercial letters of credit		257	269
Fair Value
Assets
Cash and cash equivalents		4,043	5,751
Fair value of securities held to maturity		10,103	8,412
Loans held for investment, net of allowance for loan losses	[1]	76,783	77,324
Other assets		11	11
Liabilities
Deposits		81,766	86,076
Commercial paper and other short-term borrowings		5,262	2,704
Long-term debt		8,887	7,073
Off-Balance Sheet Instruments
Commitments to extend credit and standby and commercial letters of credit		$ 257	$ 269

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