Fair Value Measurements - Narrative (Details) - USD ($) $ in Millions	3 Months Ended	9 Months Ended	12 Months Ended
	Jun. 30, 2021	Sep. 30, 2021	Dec. 31, 2020
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Settlement liability		$ 8	$ 7
DOJ Agreement
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Settlement of DOJ liability	$ 70
Settlement liability		$ 0
Residential mortgage servicing rights capitalized | Measurement input, expected term | Level 3
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Weighted average life		5 years 9 months 18 days	4 years 2 months 12 days