Derivatives and Hedging Activities - Effect of Fair Value and Cash Flow Hedges on Income (Details) - USD ($) $ in Millions		3 Months Ended		6 Months Ended
		Jun. 30, 2021	Jun. 30, 2020	Jun. 30, 2021	Jun. 30, 2020
Derivative Instruments, Gain (Loss) [Line Items]
Interest expense — Long-term debt		$ (54)	$ (71)	$ (114)	$ (161)
Interest income — Loans		888	980	1,777	2,006
Interest Income - securities		133	121	263	250
Investment banking and debt placement fees		217	156	379	272
Deposits		(16)	(96)	(37)	(265)
Other income	[1]	13	33	64	(55)
Net gain (loss) on cash flow hedging relationships
Net Gains (Losses) Reclassified From OCI Into Income		83	(89)	172	122
Interest rate | Interest expense – long-term debt | Fair Value Hedging
Net gains (losses) on fair value hedging relationships
Recognized on hedged items		(31)	(5)	173	(299)
Recognized on derivatives designated as hedging instruments		62	39	(104)	350
Net income (expense) recognized on fair value hedges		31	34	69	51
Interest rate | Interest expense – long-term debt | Cash Flow Hedging
Net gain (loss) on cash flow hedging relationships
Realized gains (losses) (pre-tax) reclassified from AOCI into net income		(1)	(1)	(2)	(2)
Net income (expense) recognized on cash flow hedges		(1)	(1)	(2)
Interest rate | Interest income – loans | Fair Value Hedging
Net gains (losses) on fair value hedging relationships
Recognized on hedged items		0	0	0	0
Recognized on derivatives designated as hedging instruments		0	0	0	0
Net income (expense) recognized on fair value hedges		0	0	0	0
Interest rate | Interest income – loans | Cash Flow Hedging
Net gain (loss) on cash flow hedging relationships
Realized gains (losses) (pre-tax) reclassified from AOCI into net income		85	90	173	124
Net Gains (Losses) Reclassified From OCI Into Income		85	90	173	124
Net income (expense) recognized on cash flow hedges		85	90	173
Interest rate | Interest Income - securities | Fair Value Hedging
Net gains (losses) on fair value hedging relationships
Recognized on hedged items		158	0	(107)	0
Recognized on derivatives designated as hedging instruments		(159)	0	108	0
Net income (expense) recognized on fair value hedges		(1)	0	1	0
Interest rate | Interest Income - securities | Cash Flow Hedging
Net gain (loss) on cash flow hedging relationships
Realized gains (losses) (pre-tax) reclassified from AOCI into net income		0	0	0	0
Net income (expense) recognized on cash flow hedges		0	0	0
Interest rate | Investment banking and debt placement fees | Fair Value Hedging
Net gains (losses) on fair value hedging relationships
Recognized on hedged items		0	0	0	0
Recognized on derivatives designated as hedging instruments		0	0	0	0
Net income (expense) recognized on fair value hedges		0	0	0	0
Interest rate | Investment banking and debt placement fees | Cash Flow Hedging
Net gain (loss) on cash flow hedging relationships
Realized gains (losses) (pre-tax) reclassified from AOCI into net income					0
Net income (expense) recognized on cash flow hedges		(1)	0	1
Interest rate | Interest expense - deposits | Fair Value Hedging
Net gains (losses) on fair value hedging relationships
Recognized on hedged items			0	0	0
Recognized on derivatives designated as hedging instruments			0	0	0
Net income (expense) recognized on fair value hedges			0	0	0
Interest rate | Interest expense - deposits | Cash Flow Hedging
Net gain (loss) on cash flow hedging relationships
Realized gains (losses) (pre-tax) reclassified from AOCI into net income		0	0	0	0
Net income (expense) recognized on cash flow hedges		0	0	0
Interest rate | Other income | Fair Value Hedging
Net gains (losses) on fair value hedging relationships
Recognized on hedged items		0	0	0	0
Recognized on derivatives designated as hedging instruments		0	0	0	0
Net income (expense) recognized on fair value hedges		0	0	0	0
Interest rate | Other income | Cash Flow Hedging
Net gain (loss) on cash flow hedging relationships
Realized gains (losses) (pre-tax) reclassified from AOCI into net income		0	0	0	0
Net income (expense) recognized on cash flow hedges		0	0	0
Interest rate | Investment banking and debt placement fees | Cash Flow Hedging
Net gain (loss) on cash flow hedging relationships
Net Gains (Losses) Reclassified From OCI Into Income		$ (1)	$ 0	$ 1	$ 0

[1] For the three and six months ended June 30, 2021, net securities gains (losses) totaled less than $1 million. For the three months ended June 30, 2021 and June 30, 2020, we did not have any impairment losses related to securities. For the three months ended June 30, 2020, we had no net securities gains (losses). For the six months ended June 30, 2020, net securities gains (losses) totaled $4 million.