Derivative Instruments and Hedging Activities - Notional and Fair Values of Derivative Instruments (Details) - USD ($) $ in Millions	Dec. 31, 2015	Dec. 31, 2014
Derivatives, Fair Value [Line Items]
Notional or Contractual Amount	$ 105,916	$ 88,645
Derivative Assets, Gross Amount	1,518	1,452
Derivative Liabilities, Gross Amount	520	339
Derivative Asset, Netting Adjustment	(532)	(624)
Derivative Liability, Netting Adjustment	(143)	(164)
Derivative Assets	986	828
Derivative Liability	377	175
Derivatives designated as accounting hedges
Derivatives, Fair Value [Line Items]
Notional or Contractual Amount	73,009	57,015
Derivative Assets, Gross Amount	1,043	996
Derivative Liabilities, Gross Amount	209	59
Derivatives designated as accounting hedges | Interest rate contracts
Derivatives, Fair Value [Line Items]
Notional or Contractual Amount	64,867	48,993
Derivative Assets, Gross Amount	717	702
Derivative Liabilities, Gross Amount	207	57
Derivatives designated as accounting hedges | Interest rate contracts | Fair value hedges
Derivatives, Fair Value [Line Items]
Notional or Contractual Amount	34,417	24,543
Derivative Assets, Gross Amount	550	480
Derivative Liabilities, Gross Amount	146	39
Derivatives designated as accounting hedges | Interest rate contracts | Cash flow hedges
Derivatives, Fair Value [Line Items]
Notional or Contractual Amount	30,450	24,450
Derivative Assets, Gross Amount	167	222
Derivative Liabilities, Gross Amount	61	18
Derivatives designated as accounting hedges | Foreign exchange contracts
Derivatives, Fair Value [Line Items]
Notional or Contractual Amount	8,142	8,022
Derivative Assets, Gross Amount	326	294
Derivative Liabilities, Gross Amount	2	2
Derivatives designated as accounting hedges | Foreign exchange contracts | Cash flow hedges
Derivatives, Fair Value [Line Items]
Notional or Contractual Amount	5,580	5,546
Derivative Assets, Gross Amount	239	221
Derivative Liabilities, Gross Amount	2	2
Derivatives designated as accounting hedges | Foreign exchange contracts | Net investment hedges
Derivatives, Fair Value [Line Items]
Notional or Contractual Amount	2,562	2,476
Derivative Assets, Gross Amount	87	73
Derivative Liabilities, Gross Amount	0	0
Derivatives not designated as accounting hedges
Derivatives, Fair Value [Line Items]
Notional or Contractual Amount	32,907	31,630
Derivative Assets, Gross Amount	475	456
Derivative Liabilities, Gross Amount	311	280
Derivatives not designated as accounting hedges | Interest rate contracts
Derivatives, Fair Value [Line Items]
Notional or Contractual Amount	32,025	31,037
Derivative Assets, Gross Amount	475	456
Derivative Liabilities, Gross Amount	307	275
Derivatives not designated as accounting hedges | Interest rate contracts | MSRs
Derivatives, Fair Value [Line Items]
Notional or Contractual Amount	1,665	777
Derivative Assets, Gross Amount	11	10
Derivative Liabilities, Gross Amount	7	3
Derivatives not designated as accounting hedges | Interest rate contracts | Customer accommodation
Derivatives, Fair Value [Line Items]
Notional or Contractual Amount	28,841	27,646
Derivative Assets, Gross Amount	431	413
Derivative Liabilities, Gross Amount	290	251
Derivatives not designated as accounting hedges | Interest rate contracts | Other interest rate exposures
Derivatives, Fair Value [Line Items]
Notional or Contractual Amount	1,519	2,614
Derivative Assets, Gross Amount	33	33
Derivative Liabilities, Gross Amount	10	21
Derivatives not designated as accounting hedges | Other contracts
Derivatives, Fair Value [Line Items]
Notional or Contractual Amount	882	593
Derivative Assets, Gross Amount	0	0
Derivative Liabilities, Gross Amount	$ 4	$ 5