Fair Value Measurement and Fair Value of Financial Instruments (Details 5) - USD ($) $ in Millions		Mar. 31, 2017	Dec. 31, 2016
Assets
Federal Funds Sold and Securities Borrowed or Purchased under Agreements to Resell, Fair Value Disclosure		$ 19,992	$ 19,747
Fair value of securities held to maturity		10,348	10,316
Liabilities
Securities loaned or sold under repurchase agreements		25,079	24,616
Level 1
Assets
Cash and cash equivalents		4,827	5,753
Federal Funds Sold and Securities Borrowed or Purchased under Agreements to Resell, Fair Value Disclosure		0	0
Fair value of securities held to maturity		0	0
Loans held for investment, net of allowance for loan losses		0	0
Liabilities
Deposits		0	0
Commercial paper and other short-term borrowings		0	0
Securities loaned or sold under repurchase agreements		0	0
Long-term debt		0	0
Off-Balance Sheet Instruments
Commitments to extend credit and standby and commercial letters of credit		0	0
Level 2
Assets
Cash and cash equivalents		0	0
Federal Funds Sold and Securities Borrowed or Purchased under Agreements to Resell, Fair Value Disclosure		19,992	19,747
Fair value of securities held to maturity		10,348	10,316
Loans held for investment, net of allowance for loan losses		0	0
Liabilities
Deposits		86,519	86,930
Commercial paper and other short-term borrowings		3,487	2,360
Securities loaned or sold under repurchase agreements		25,079	24,616
Long-term debt		11,348	11,411
Off-Balance Sheet Instruments
Commitments to extend credit and standby and commercial letters of credit		0	0
Level 3
Assets
Cash and cash equivalents		0	0
Federal Funds Sold and Securities Borrowed or Purchased under Agreements to Resell, Fair Value Disclosure		0	0
Fair value of securities held to maturity		0	0
Loans held for investment, net of allowance for loan losses	[1]	77,234	76,257
Liabilities
Deposits		0	0
Commercial paper and other short-term borrowings		0	0
Securities loaned or sold under repurchase agreements		0	0
Long-term debt		0	0
Off-Balance Sheet Instruments
Commitments to extend credit and standby and commercial letters of credit		202	221
Carrying Amount
Assets
Cash and cash equivalents		4,827	5,753
Federal Funds Sold and Securities Borrowed or Purchased under Agreements to Resell, Fair Value Disclosure		19,992	19,747
Fair value of securities held to maturity		10,374	10,337
Loans held for investment, net of allowance for loan losses	[1]	76,105	75,112
Liabilities
Deposits		86,533	86,947
Commercial paper and other short-term borrowings		3,487	2,360
Securities loaned or sold under repurchase agreements		25,079	24,616
Long-term debt		11,333	11,410
Off-Balance Sheet Instruments
Commitments to extend credit and standby and commercial letters of credit		202	221
Fair Value
Assets
Cash and cash equivalents		4,827	5,753
Federal Funds Sold and Securities Borrowed or Purchased under Agreements to Resell, Fair Value Disclosure		19,992	19,747
Fair value of securities held to maturity		10,348	10,316
Loans held for investment, net of allowance for loan losses	[1]	77,234	76,257
Liabilities
Deposits		86,519	86,930
Commercial paper and other short-term borrowings		3,487	2,360
Securities loaned or sold under repurchase agreements		25,079	24,616
Long-term debt		11,348	11,411
Off-Balance Sheet Instruments
Commitments to extend credit and standby and commercial letters of credit		$ 202	$ 221

[1] Excludes lease financing. The carrying amount is net of the allowance for loan and lease losses.