Fair Value Measurements - Carrying Amount and Estimated Fair Value of Financial Instruments (Details) - Nonrecurring - Level 3 - USD ($) $ in Millions	Mar. 31, 2020	Dec. 31, 2019
Residential first mortgage loans
Fair Value Inputs, Assets, Quantitative Information
Loans held-for-investment	$ 15	$ 14
Repossessed assets
Fair Value Inputs, Assets, Quantitative Information
Loans held-for-investment	$ 10	$ 10

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