Mortgage Servicing Rights and Related Liabilities - Reverse MSRs and Liabilities - Amortized Cost (Details) - USD ($) $ in Millions	3 Months Ended
	Mar. 31, 2021	Mar. 31, 2020
Servicing Asset at Amortized Cost, Balance [Roll Forward]
Fair value - end of period	$ 3,354
Servicing Liability at Amortized Cost [Roll Forward]
Balance - beginning of period	41
Balance - end of the period	38
Reverse MSRs
Servicing Asset at Amortized Cost, Balance [Roll Forward]
Balance - beginning of period	5	$ 6
Amortization/accretion	0	0
Balance - end of the period	5	6
Fair value - end of period	5	6
Reverse MSLs
Servicing Liability at Amortized Cost [Roll Forward]
Balance - beginning of period	41	61
Amortization/accretion	(3)	(8)
Balance - end of the period	38	53
Fair value - end of period	$ 38	$ 27