Fair Value Measures - Roll Forward of Financial Instruments (Details) - Significant Unobservable Inputs (Level 3) - USD ($) $ in Millions	3 Months Ended	9 Months Ended
	Sep. 30, 2023	Sep. 30, 2023
Fair Value, Assets Measured on Recurring Basis, Unobservable Input Reconciliation, Calculation [Roll Forward]
Balance at Beginning of Year	$ 1,031	$ 1,032
Total Gains / (Losses) Recorded in Earnings	(5)	(65)
Purchases / Originations	97	238
Sales	0	(51)
Settlement	0	0
Transfers In (Out)	38	7
Balance at End of Year	1,161	1,161
Mortgage servicing rights
Fair Value, Assets Measured on Recurring Basis, Unobservable Input Reconciliation, Calculation [Roll Forward]
Balance at Beginning of Year	1,031	1,033
Total Gains / (Losses) Recorded in Earnings	37	5
Purchases / Originations	67	148
Sales	0	(51)
Settlement	0	0
Transfers In (Out)	0	0
Balance at End of Year	1,135	1,135
Private Label CMOs
Fair Value, Assets Measured on Recurring Basis, Unobservable Input Reconciliation, Calculation [Roll Forward]
Balance at Beginning of Year	0	0
Total Gains / (Losses) Recorded in Earnings	0	0
Purchases / Originations	0	0
Sales	0	0
Settlement	0	0
Transfers In (Out)	32	32
Balance at End of Year	32	32
Rate lock commitments
Fair Value, Assets Measured on Recurring Basis, Unobservable Input Reconciliation, Calculation [Roll Forward]
Balance at Beginning of Year	0	(1)
Total Gains / (Losses) Recorded in Earnings	(42)	(70)
Purchases / Originations	30	90
Sales	0	0
Settlement	0	0
Transfers In (Out)	6	(25)
Balance at End of Year	$ (6)	$ (6)