Derivative Instruments and Hedging Activities - Notional and Fair Values of Derivative Instruments (Details) - USD ($) $ in Millions	Mar. 31, 2019	Dec. 31, 2018
Derivatives, Fair Value [Line Items]
Notional or contractual amount	$ 218,973	$ 212,505
Derivative assets, gross amount	1,221	1,539
Derivative liabilities, gross amount	875	1,201
Derivative asset, netting adjustments	(512)	(1,079)
Derivative liability, netting adjustments	(421)	(287)
Total derivative assets	709	460
Total derivative liabilities	454	914
Cumulative CVA balance	7	3
Cumulative DVA balance	1	1
Derivatives designated as accounting hedges
Derivatives, Fair Value [Line Items]
Notional or contractual amount	145,506	142,965
Derivative assets, gross amount	236	509
Derivative liabilities, gross amount	138	100
Derivatives designated as accounting hedges | Interest rate contracts
Derivatives, Fair Value [Line Items]
Notional or contractual amount	137,335	134,613
Derivative assets, gross amount	162	147
Derivative liabilities, gross amount	111	98
Derivatives designated as accounting hedges | Interest rate contracts | Fair value hedges
Derivatives, Fair Value [Line Items]
Notional or contractual amount	52,735	53,413
Derivative assets, gross amount	24	64
Derivative liabilities, gross amount	67	28
Derivatives designated as accounting hedges | Interest rate contracts | Cash flow hedges
Derivatives, Fair Value [Line Items]
Notional or contractual amount	84,600	81,200
Derivative assets, gross amount	138	83
Derivative liabilities, gross amount	44	70
Derivatives designated as accounting hedges | Foreign exchange contracts
Derivatives, Fair Value [Line Items]
Notional or contractual amount	8,171	8,352
Derivative assets, gross amount	74	362
Derivative liabilities, gross amount	27	2
Derivatives designated as accounting hedges | Foreign exchange contracts | Cash flow hedges
Derivatives, Fair Value [Line Items]
Notional or contractual amount	5,523	5,745
Derivative assets, gross amount	42	184
Derivative liabilities, gross amount	21	2
Derivatives designated as accounting hedges | Foreign exchange contracts | Net investment hedges
Derivatives, Fair Value [Line Items]
Notional or contractual amount	2,648	2,607
Derivative assets, gross amount	32	178
Derivative liabilities, gross amount	6	0
Derivatives not designated as accounting hedges
Derivatives, Fair Value [Line Items]
Notional or contractual amount	73,467	69,540
Derivative assets, gross amount	985	1,030
Derivative liabilities, gross amount	737	1,101
Derivatives not designated as accounting hedges | Customer accommodation
Derivatives, Fair Value [Line Items]
Notional or contractual amount	63,781	61,477
Derivative assets, gross amount	866	999
Derivative liabilities, gross amount	702	1,053
Derivatives not designated as accounting hedges | Interest rate contracts | Customer accommodation
Derivatives, Fair Value [Line Items]
Notional or contractual amount	50,554	49,386
Derivative assets, gross amount	295	190
Derivative liabilities, gross amount	160	256
Derivatives not designated as accounting hedges | Interest rate contracts | Other interest rate exposures
Derivatives, Fair Value [Line Items]
Notional or contractual amount	6,065	6,427
Derivative assets, gross amount	30	29
Derivative liabilities, gross amount	24	36
Derivatives not designated as accounting hedges | Foreign exchange contracts | Customer accommodation
Derivatives, Fair Value [Line Items]
Notional or contractual amount	1,698	1,418
Derivative assets, gross amount	18	12
Derivative liabilities, gross amount	15	11
Derivatives not designated as accounting hedges | Commodity contracts | Customer accommodation
Derivatives, Fair Value [Line Items]
Notional or contractual amount	11,529	10,673
Derivative assets, gross amount	553	797
Derivative liabilities, gross amount	527	786
Derivatives not designated as accounting hedges | Other contracts
Derivatives, Fair Value [Line Items]
Notional or contractual amount	3,621	1,636
Derivative assets, gross amount	89	2
Derivative liabilities, gross amount	$ 11	$ 12