Fair Value Measurements - Level 3 Reconciliation (Details) - USD ($) $ in Millions	6 Months Ended
	Jun. 30, 2019	Jun. 30, 2018
Excess spread financing
Fair Value, Liabilities Measured on Recurring Basis, Unobservable Input Reconciliation, Calculation [Roll Forward]
Balance - beginning of period	$ 1,184	$ 996
Total gains or losses included in earnings	(74)	74
Payments received from borrowers	0
Purchases	0	0
Issuances	438	70
Sales	0	0
Repayments	(12)	(2)
Settlements	(107)	(91)
Balance - end of period	1,429	1,047
Mortgage servicing rights financing
Fair Value, Liabilities Measured on Recurring Basis, Unobservable Input Reconciliation, Calculation [Roll Forward]
Balance - beginning of period	32	10
Total gains or losses included in earnings	11	6
Payments received from borrowers	0
Purchases	0	0
Issuances	0	0
Sales	0	0
Repayments	0	0
Settlements	0	0
Balance - end of period	43	16
Mortgage servicing rights
Fair Value, Assets Measured on Recurring Basis, Unobservable Input Reconciliation, Calculation [Roll Forward]
Balance - beginning of period	3,665	2,937
Total gains or losses included in earnings	(724)	144
Payments received from borrowers	0
Purchases	689	132
Issuances	169	139
Sales	(294)	4
Repayments	0	0
Settlements	0	0
Balance - end of period	3,505	$ 3,356
Mortgage loans held for investment
Fair Value, Assets Measured on Recurring Basis, Unobservable Input Reconciliation, Calculation [Roll Forward]
Balance - beginning of period	119
Total gains or losses included in earnings	3
Payments received from borrowers	(8)
Purchases	0
Issuances	0
Sales	0
Repayments	0
Settlements	0
Balance - end of period	$ 114