Derivative Instruments and Hedging Activities - Notional and Fair Values of Derivative Instruments (Details) - USD ($) $ in Millions	Dec. 31, 2017	Dec. 31, 2016
Derivatives, Fair Value [Line Items]
Cumulative counterparty credit risk valuation adjustment	$ 2	$ 6
Notional or Contractual Amount	196,612	142,938
Derivative Assets, Gross Amount	1,040	1,494
Derivative Liabilities, Gross Amount	1,268	1,438
Derivative Asset, Netting Adjustment	(275)	(539)
Derivative Liability, Netting Adjustment	(662)	(336)
Derivative Assets	765	955
Derivative Liability	606	1,102
Cumulative credit risk valuation adjustment related to our credit quality (less than $1 million	1	1
Increase in derivative assets due to CME Rulebook change	38
Decrease in derivative liabilities due to CME Rulebook change	724
Derivatives designated as accounting hedges
Derivatives, Fair Value [Line Items]
Notional or Contractual Amount	143,026	98,896
Derivative Assets, Gross Amount	152	717
Derivative Liabilities, Gross Amount	528	865
Derivatives designated as accounting hedges | Interest rate contracts
Derivatives, Fair Value [Line Items]
Notional or Contractual Amount	133,904	90,880
Derivative Assets, Gross Amount	132	446
Derivative Liabilities, Gross Amount	289	856
Derivatives designated as accounting hedges | Interest rate contracts | Fair value hedges
Derivatives, Fair Value [Line Items]
Notional or Contractual Amount	56,604	40,480
Derivative Assets, Gross Amount	102	295
Derivative Liabilities, Gross Amount	164	569
Derivatives designated as accounting hedges | Interest rate contracts | Cash flow hedges
Derivatives, Fair Value [Line Items]
Notional or Contractual Amount	77,300	50,400
Derivative Assets, Gross Amount	30	151
Derivative Liabilities, Gross Amount	125	287
Derivatives designated as accounting hedges | Foreign exchange contracts
Derivatives, Fair Value [Line Items]
Notional or Contractual Amount	9,122	8,016
Derivative Assets, Gross Amount	20	271
Derivative Liabilities, Gross Amount	239	9
Derivatives designated as accounting hedges | Foreign exchange contracts | Cash flow hedges
Derivatives, Fair Value [Line Items]
Notional or Contractual Amount	6,086	5,620
Derivative Assets, Gross Amount	19	108
Derivative Liabilities, Gross Amount	75	9
Derivatives designated as accounting hedges | Foreign exchange contracts | Net investment hedges
Derivatives, Fair Value [Line Items]
Notional or Contractual Amount	3,036	2,396
Derivative Assets, Gross Amount	1	163
Derivative Liabilities, Gross Amount	164	0
Derivatives not designated as accounting hedges
Derivatives, Fair Value [Line Items]
Notional or Contractual Amount	53,586	44,042
Derivative Assets, Gross Amount	888	777
Derivative Liabilities, Gross Amount	740	573
Derivatives not designated as accounting hedges | Interest rate contracts
Derivatives, Fair Value [Line Items]
Notional or Contractual Amount	52,377	42,275
Derivative Assets, Gross Amount	888	720
Derivative Liabilities, Gross Amount	735	559
Derivatives not designated as accounting hedges | Interest rate contracts | MSRs
Derivatives, Fair Value [Line Items]
Notional or Contractual Amount	1,033	1,696
Derivative Assets, Gross Amount	7	17
Derivative Liabilities, Gross Amount	1	21
Derivatives not designated as accounting hedges | Interest rate contracts | Customer accommodation
Derivatives, Fair Value [Line Items]
Notional or Contractual Amount	48,520	39,474
Derivative Assets, Gross Amount	848	670
Derivative Liabilities, Gross Amount	727	530
Derivatives not designated as accounting hedges | Interest rate contracts | Other interest rate exposures
Derivatives, Fair Value [Line Items]
Notional or Contractual Amount	2,824	1,105
Derivative Assets, Gross Amount	33	33
Derivative Liabilities, Gross Amount	7	8
Derivatives not designated as accounting hedges | Other contracts
Derivatives, Fair Value [Line Items]
Notional or Contractual Amount	1,209	1,767
Derivative Assets, Gross Amount	0	57
Derivative Liabilities, Gross Amount	$ 5	$ 14