Amount of the excess of a loan's cash flows expected to be collected over the investor's initial investment in acquired loans not accounted for as debt securities with evidence of deterioration of credit quality.

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Loans and Allowance for Loan Losses - Accretable Yield for Purchased Credit-Impaired Loans (Details) - USD ($) $ in Millions	12 Months Ended
	Dec. 31, 2016	Dec. 31, 2015	Dec. 31, 2014
Certain Loans Acquired in Transfer Not Accounted for as Debt Securities, Accretable Yield Movement Schedule [Roll Forward]
Accretable yield, beginning of period	$ 195	$ 288	$ 378
Additions	0	0	0
Accretion	(96)	(151)	(268)
Reclassifications from nonaccretable difference during the period	55	58	178
Accretable yield, end of period	154	195	$ 288
Concentrations of Credit Risk
Loans	77,551	79,257
Consumer
Concentrations of Credit Risk
Loans	33,328	30,595
Consumer \| Residential mortgage \| Loans Receivable
Concentrations of Credit Risk
Loans	29,800
Commercial
Concentrations of Credit Risk
Loans	43,986	$ 48,326
Commercial \| Loans Receivable \| Financial and Insurance
Concentrations of Credit Risk
Loans	4,800
Additional unfunded commitments to extend credit	5,200
Commercial \| Loans Receivable \| Power and utilities
Concentrations of Credit Risk
Loans	4,100
Additional unfunded commitments to extend credit	6,100
Commercial \| Loans Receivable \| Oil and gas
Concentrations of Credit Risk
Loans	2,000
Additional unfunded commitments to extend credit	2,300
Commercial \| Loans Receivable \| Manufacturing
Concentrations of Credit Risk
Loans	4,000
Additional unfunded commitments to extend credit	3,200
Commercial \| Commercial mortgage \| Loans Receivable
Concentrations of Credit Risk
Loans	16,400
Additional unfunded commitments to extend credit	$ 5,100