Derivatives and Hedging Activities - Effect of Fair Value and Cash Flow Hedges on Income (Details) - USD ($) $ in Millions		3 Months Ended		9 Months Ended
		Sep. 30, 2020	Sep. 30, 2019	Sep. 30, 2020	Sep. 30, 2019
Derivative Instruments, Gain (Loss) [Line Items]
Interest expense — Long-term debt		$ 64	$ 114	$ 225	$ 354
Interest income — Loans		927	1,073	2,933	3,221
Deposits		54	227	319	652
Other income	[1]	28	27	(27)	54
Interest rate | Interest expense – long-term debt | Fair Value Hedging
Net gains (losses) on fair value hedging relationships
Recognized on hedged items		47	(75)	(252)	(320)
Recognized on derivatives designated as hedging instruments		(7)	72	343	296
Net income (expense) recognized on fair value hedges		40	(3)	91	(24)
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)	(3)	(2)
Net income (expense) recognized on cash flow hedges		(1)	(1)	(3)
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		100	(8)	224	(51)
Net income (expense) recognized on cash flow hedges		100	(8)	224
Interest rate | Interest expense - deposits | Fair Value Hedging
Net gains (losses) on fair value hedging relationships
Recognized on hedged items		0	0	0	(1)
Recognized on derivatives designated as hedging instruments		0	0	0	0
Net income (expense) recognized on fair value hedges		0	0	0	(1)
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

[1] For the three months ended September 30, 2020, we had no net securities gains (losses). For the nine months ended September 30, 2020, net securities gains (losses) totaled $4 million. For the three and nine months ended September 30, 2019, net securities gains (losses) totaled less than $15 million. For the three and nine months ended September 30, 2020, and September 30, 2019, we did not have any impairment losses related to securities.