Fair Value Measurements - Quantitative Information about Nonrecurring Level 3 Fair Value Financial Instruments (Details) - Nonrecurring - Level 3 $ in Millions	Dec. 31, 2019 USD ($) loss_severity_discount_per_loan	Dec. 31, 2018 USD ($) loss_severity_discount_per_loan
Residential first mortgage
Fair Value Inputs, Assets, Quantitative Information
Loans held-for-investment | $	$ 14	$ 12
Repossessed assets
Fair Value Inputs, Assets, Quantitative Information
Loans held-for-investment | $	$ 10	$ 7
Loss severity discount | Residential first mortgage | Range (Weighted Average)
Fair Value Inputs, Assets, Quantitative Information
Loans held for investment, fair value input (in percentage)	0.25	0.25
Loss severity discount | Residential first mortgage | High Range
Fair Value Inputs, Assets, Quantitative Information
Loans held for investment, fair value input (in percentage)	0.30	0.30
Loss severity discount | Residential first mortgage | Weighted Average
Fair Value Inputs, Assets, Quantitative Information
Loans held for investment, fair value input (in percentage)	0.259	0.283
Loss severity discount | Repossessed assets | Range (Weighted Average)
Fair Value Inputs, Assets, Quantitative Information
Repossessed asset, fair value input (as a percent)	0.00	0.00
Loss severity discount | Repossessed assets | High Range
Fair Value Inputs, Assets, Quantitative Information
Repossessed asset, fair value input (as a percent)	1	1
Loss severity discount | Repossessed assets | Weighted Average
Fair Value Inputs, Assets, Quantitative Information
Repossessed asset, fair value input (as a percent)	0.171	0.258