Derivative Instruments and Hedging Activities (Narrative) (Details) - USD ($) $ in Millions	Dec. 31, 2023	Sep. 30, 2023	Dec. 31, 2022
Derivative Instruments, Gain (Loss) [Line Items]
Subordinated notes, Par amount	$ 588
Derivative, notional amount	22,148		$ 24,498
Deferred gain (loss) in OCI	201
Derivative liability, fair value	333		451
Cash collateral pledged for derivative liabilities	2
Additional collateral that would be required to be pledge if credit rating was downgraded by one notch	0
Subordinated Notes, Interest Rate 3.25%
Derivative Instruments, Gain (Loss) [Line Items]
Subordinated notes, Par amount	500
Other liabilities
Derivative Instruments, Gain (Loss) [Line Items]
Derivative liability, fair value	333		451
Derivatives designated as hedges
Derivative Instruments, Gain (Loss) [Line Items]
Derivative, notional amount	6,521		9,361
Derivatives designated as hedges | Other liabilities
Derivative Instruments, Gain (Loss) [Line Items]
Derivative liability, fair value	0		1
Fair Value Hedging | Derivatives designated as hedges | Interest rate swaps
Derivative Instruments, Gain (Loss) [Line Items]
Derivative, notional amount	0		500
Fair Value Hedging | Derivatives designated as hedges | Asset hedges: Pay-fixed interest rate swaps 1
Derivative Instruments, Gain (Loss) [Line Items]
Derivative, notional amount	4,571		1,228
Fair Value Hedging | Derivatives designated as hedges | Pay-Fixed, Receive-Floating Swap
Derivative Instruments, Gain (Loss) [Line Items]
Derivative, notional amount		$ 1,000
Fair Value Hedging | Derivatives designated as hedges | Asset Hedge, Pay-Fixed, Receive Floating Interest Rate Swap
Derivative Instruments, Gain (Loss) [Line Items]
Derivative, notional amount	1,100
Fair Value Hedging | Derivatives designated as hedges | Other liabilities | Interest rate swaps
Derivative Instruments, Gain (Loss) [Line Items]
Derivative liability, fair value	0		0
Fair Value Hedging | Derivatives designated as hedges | Other liabilities | Asset hedges: Pay-fixed interest rate swaps 1
Derivative Instruments, Gain (Loss) [Line Items]
Derivative liability, fair value	0		0
Cash Flow Hedging
Derivative Instruments, Gain (Loss) [Line Items]
Subordinated notes, Par amount	5,000
Cash Flow Hedging | Derivatives designated as hedges | Interest rate swaps
Derivative Instruments, Gain (Loss) [Line Items]
Derivative, notional amount	1,450		7,633
Cash Flow Hedging | Derivatives designated as hedges | Pay-Fixed Interest Rate Swap
Derivative Instruments, Gain (Loss) [Line Items]
Derivative, notional amount		$ 2,500
Cash Flow Hedging | Derivatives designated as hedges | Other liabilities | Interest rate swaps
Derivative Instruments, Gain (Loss) [Line Items]
Derivative liability, fair value	$ 0		$ 1