Loans and Allowance for Credit Losses, Troubled Debt Restructurings, Current Defaults (Details) - USD ($) $ in Millions	3 Months Ended		6 Months Ended
	Jun. 30, 2017	Jun. 30, 2016	Jun. 30, 2017	Jun. 30, 2016
Financing Receivable, Modifications [Line Items]
Recorded investment of defaults	$ 93	$ 103	$ 224	$ 203
Commercial Portfolio Segment [Member]
Financing Receivable, Modifications [Line Items]
Recorded investment of defaults	40	52	123	99
Commercial and Industrial Loans [Member]
Financing Receivable, Modifications [Line Items]
Recorded investment of defaults	30	20	92	45
Commercial real estate mortgage [Member]
Financing Receivable, Modifications [Line Items]
Recorded investment of defaults	10	31	31	51
Commercial Real Estate Construction [Member]
Financing Receivable, Modifications [Line Items]
Recorded investment of defaults	0	1	0	3
Consumer Portfolio Segment [Member]
Financing Receivable, Modifications [Line Items]
Recorded investment of defaults	53	51	101	104
Real estate 1-4 family first mortgage [Member]
Financing Receivable, Modifications [Line Items]
Recorded investment of defaults	26	30	51	61
Real estate 1-4 family junior lien mortgage [Member]
Financing Receivable, Modifications [Line Items]
Recorded investment of defaults	5	4	9	9
Credit Card [Member]
Financing Receivable, Modifications [Line Items]
Recorded investment of defaults	17	13	32	26
Automobile [Member]
Financing Receivable, Modifications [Line Items]
Recorded investment of defaults	4	3	7	6
Other revolving credit and installment [Member]
Financing Receivable, Modifications [Line Items]
Recorded investment of defaults	$ 1	$ 1	$ 2	$ 2