Mortgage Banking Activity - Residential Mortgage Loans (Details) - USD ($) $ in Millions	6 Months Ended
	Jun. 30, 2021	Jun. 30, 2020
Loans Receivable Held-for-sale, Net, Reconciliation to Cash Flow [Roll Forward]
Balance at beginning of period	$ 1,022
Acquired	0	$ 320
Originations and purchases	1,420	2,499
Sales, net of gains	(1,489)	(2,405)
Mortgage loans transferred from (to) held for investment	30	(9)
Balance at end of period	977
Mortgage loans
Loans Receivable Held-for-sale, Net, Reconciliation to Cash Flow [Roll Forward]
Balance at beginning of period	409	4
Balance at end of period	$ 370	$ 409