Derivative Instruments and Hedging Activities (Notional and Recorded Fair Values) (Details) - USD ($)	Sep. 30, 2021	Dec. 31, 2020
Derivative [Line Items]
Notional amount	$ 20,796,000,000	$ 17,877,000,000
Other assets	262,000,000	418,000,000
Other liabilities	45,000,000	38,000,000
Net credit valuation adjustment reducing fair value	3,000,000	18,000,000
Other assets
Derivative [Line Items]
Other assets	287,000,000	420,000,000
Other liabilities
Derivative [Line Items]
Other liabilities	270,000,000	418,000,000
Derivatives designated as hedges
Derivative [Line Items]
Notional amount	6,266,000,000	4,033,000,000
Derivatives designated as hedges | Other assets
Derivative [Line Items]
Other assets	10,000,000	3,000,000
Derivatives designated as hedges | Other liabilities
Derivative [Line Items]
Other liabilities	0	0
Derivatives designated as hedges | Interest rate swaps | Cash Flow Hedging
Derivative [Line Items]
Notional amount	5,383,000,000	3,150,000,000
Derivatives designated as hedges | Interest rate swaps | Fair Value Hedging
Derivative [Line Items]
Notional amount	500,000,000	500,000,000
Derivatives designated as hedges | Interest rate swaps | Other assets | Cash Flow Hedging
Derivative [Line Items]
Other assets	0	0
Derivatives designated as hedges | Interest rate swaps | Other assets | Fair Value Hedging
Derivative [Line Items]
Other assets	0	0
Derivatives designated as hedges | Interest rate swaps | Other liabilities | Cash Flow Hedging
Derivative [Line Items]
Other liabilities	0	0
Derivatives designated as hedges | Interest rate swaps | Other liabilities | Fair Value Hedging
Derivative [Line Items]
Other liabilities	0	0
Derivatives designated as hedges | Asset hedges: Pay-fixed interest rate swaps | Fair Value Hedging
Derivative [Line Items]
Notional amount	383,000,000	383,000,000
Derivatives designated as hedges | Asset hedges: Pay-fixed interest rate swaps | Other assets | Fair Value Hedging
Derivative [Line Items]
Other assets	10,000,000	3,000,000
Derivatives designated as hedges | Asset hedges: Pay-fixed interest rate swaps | Other liabilities | Fair Value Hedging
Derivative [Line Items]
Other liabilities	0	0
Derivatives not designated as hedging instruments
Derivative [Line Items]
Notional amount	14,530,000,000	13,844,000,000
Derivatives not designated as hedging instruments | Other assets
Derivative [Line Items]
Other assets	277,000,000	417,000,000
Derivatives not designated as hedging instruments | Other liabilities
Derivative [Line Items]
Other liabilities	270,000,000	418,000,000
Derivatives not designated as hedging instruments | Customer-facing interest rate derivatives
Derivative [Line Items]
Notional amount	6,334,000,000	5,986,000,000
Derivatives not designated as hedging instruments | Customer-facing interest rate derivatives | Other assets
Derivative [Line Items]
Other assets	235,000,000	390,000,000
Derivatives not designated as hedging instruments | Customer-facing interest rate derivatives | Other liabilities
Derivative [Line Items]
Other liabilities	25,000,000	2,000,000
Derivatives not designated as hedging instruments | Offsetting interest rate derivatives
Derivative [Line Items]
Notional amount	6,334,000,000	5,986,000,000
Derivatives not designated as hedging instruments | Offsetting interest rate derivatives | Other assets
Derivative [Line Items]
Other assets	28,000,000	3,000,000
Derivatives not designated as hedging instruments | Offsetting interest rate derivatives | Other assets | Fair Value Hedging
Derivative [Line Items]
Other assets	3,000,000	1,000,000
Derivatives not designated as hedging instruments | Offsetting interest rate derivatives | Other liabilities
Derivative [Line Items]
Other liabilities	241,000,000	409,000,000
Derivatives not designated as hedging instruments | Offsetting interest rate derivatives | Other liabilities | Fair Value Hedging
Derivative [Line Items]
Other liabilities	16,000,000	29,000,000
Derivatives not designated as hedging instruments | Other interest rate derivatives
Derivative [Line Items]
Notional amount	1,476,000,000	1,649,000,000
Derivatives not designated as hedging instruments | Other interest rate derivatives | Other assets
Derivative [Line Items]
Other assets	10,000,000	20,000,000
Derivatives not designated as hedging instruments | Other interest rate derivatives | Other liabilities
Derivative [Line Items]
Other liabilities	0	3,000,000
Derivatives not designated as hedging instruments | Foreign exchange derivatives
Derivative [Line Items]
Notional amount	386,000,000	223,000,000
Derivatives not designated as hedging instruments | Foreign exchange derivatives | Other assets
Derivative [Line Items]
Other assets	4,000,000	4,000,000
Derivatives not designated as hedging instruments | Foreign exchange derivatives | Other liabilities
Derivative [Line Items]
Other liabilities	$ 4,000,000	$ 4,000,000