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.

Reference 1: http://www.xbrl.org/2003/role/presentationRef
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Amount of decrease from accretion 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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Reference 1: http://www.xbrl.org/2003/role/presentationRef
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Amount of additions to 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, 2015	Dec. 31, 2014	Dec. 31, 2013
Certain Loans Acquired in Transfer Not Accounted for as Debt Securities, Accretable Yield Movement Schedule [Roll Forward]
Accretable yield, beginning of period	$ 288	$ 378	$ 590
Additions	0	0	31
Accretion	(151)	(268)	(336)
Reclassifications from nonaccretable difference during the period	58	178	93
Accretable yield, end of period	195	288	$ 378
Concentrations of Credit Risk
Loans	77,599	76,804
Consumer portfolio
Concentrations of Credit Risk
Loans		32,094
Consumer portfolio \| Residential mortgage \| Loans Receivable
Concentrations of Credit Risk
Loans	27,300
Commercial portfolio
Concentrations of Credit Risk
Loans	46,668	$ 44,185
Commercial portfolio \| Commercial mortgage \| Loans Receivable
Concentrations of Credit Risk
Loans	16,700
Additional unfunded commitments to extend credit	5,400
Commercial portfolio \| Commercial and Industrial Sector [Member] \| Loans Receivable \| Financial and Insurance [Member]
Concentrations of Credit Risk
Loans	6,500
Additional unfunded commitments to extend credit	4,500
Commercial portfolio \| Commercial and Industrial Sector [Member] \| Loans Receivable \| Power and utilities
Concentrations of Credit Risk
Loans	4,500
Additional unfunded commitments to extend credit	6,800
Commercial portfolio \| Commercial and Industrial Sector [Member] \| Loans Receivable \| Oil and gas
Concentrations of Credit Risk
Loans	3,700
Additional unfunded commitments to extend credit	3,700
Commercial portfolio \| Commercial and Industrial Sector [Member] \| Loans Receivable \| Manufacturing
Concentrations of Credit Risk
Loans	3,700
Additional unfunded commitments to extend credit	$ 3,600