Fair Value Measurements - Quantitative Information about Recurring Level 3 Fair Value Instruments (Details) - Recurring - Level 3 $ in Millions	Jun. 30, 2019 USD ($) $ / loan	Dec. 31, 2018 USD ($) $ / loan
Home equity
Fair Value Inputs, Assets and Liabilities, Quantitative Information [Line Items]
Loans held-for-investment	$ 2	$ 2
Home equity | Discount rate | Lower range
Fair Value Inputs, Assets and Liabilities, Quantitative Information [Line Items]
Loans held for investment, fair value input	0.072	0.072
Home equity | Discount rate | Upper range
Fair Value Inputs, Assets and Liabilities, Quantitative Information [Line Items]
Loans held for investment, fair value input	0.108	0.108
Home equity | Discount rate | Weighted Average
Fair Value Inputs, Assets and Liabilities, Quantitative Information [Line Items]
Loans held for investment, fair value input	0.090	0.090
Home equity | Constant prepayment rate | Lower range
Fair Value Inputs, Assets and Liabilities, Quantitative Information [Line Items]
Loans held for investment, fair value input	0.138	0.136
Home equity | Constant prepayment rate | Upper range
Fair Value Inputs, Assets and Liabilities, Quantitative Information [Line Items]
Loans held for investment, fair value input	0.206	0.203
Home equity | Constant prepayment rate | Weighted Average
Fair Value Inputs, Assets and Liabilities, Quantitative Information [Line Items]
Loans held for investment, fair value input	0.172	0.169
Home equity | Constant default rate | Lower range
Fair Value Inputs, Assets and Liabilities, Quantitative Information [Line Items]
Loans held for investment, fair value input	0.030	0.030
Home equity | Constant default rate | Upper range
Fair Value Inputs, Assets and Liabilities, Quantitative Information [Line Items]
Loans held for investment, fair value input	0.045	0.046
Home equity | Constant default rate | Weighted Average
Fair Value Inputs, Assets and Liabilities, Quantitative Information [Line Items]
Loans held for investment, fair value input	0.037	0.038
Mortgage servicing rights
Fair Value Inputs, Assets and Liabilities, Quantitative Information [Line Items]
Mortgage servicing rights	$ 316	$ 290
Mortgage servicing rights | Constant prepayment rate | Lower range
Fair Value Inputs, Assets and Liabilities, Quantitative Information [Line Items]
Weighted average cost to service per loan	0.000	0.000
Mortgage servicing rights | Constant prepayment rate | Upper range
Fair Value Inputs, Assets and Liabilities, Quantitative Information [Line Items]
Weighted average cost to service per loan	0.125	0.107
Mortgage servicing rights | Constant prepayment rate | Weighted Average
Fair Value Inputs, Assets and Liabilities, Quantitative Information [Line Items]
Weighted average cost to service per loan	0.106	0.096
Mortgage servicing rights | Weighted average cost to service per loan | Lower range
Fair Value Inputs, Assets and Liabilities, Quantitative Information [Line Items]
Weighted average cost to service per loan | $ / loan	68	67
Mortgage servicing rights | Weighted average cost to service per loan | Upper range
Fair Value Inputs, Assets and Liabilities, Quantitative Information [Line Items]
Weighted average cost to service per loan | $ / loan	95	95
Mortgage servicing rights | Weighted average cost to service per loan | Weighted Average
Fair Value Inputs, Assets and Liabilities, Quantitative Information [Line Items]
Weighted average cost to service per loan | $ / loan	85	86
Mortgage servicing rights | Option adjusted spread | Lower range
Fair Value Inputs, Assets and Liabilities, Quantitative Information [Line Items]
Weighted average cost to service per loan	0.023	0.021
Mortgage servicing rights | Option adjusted spread | Upper range
Fair Value Inputs, Assets and Liabilities, Quantitative Information [Line Items]
Weighted average cost to service per loan	0.259	0.259
Mortgage servicing rights | Option adjusted spread | Weighted Average
Fair Value Inputs, Assets and Liabilities, Quantitative Information [Line Items]
Weighted average cost to service per loan	0.054	0.054
Rate lock commitments
Fair Value Inputs, Assets and Liabilities, Quantitative Information [Line Items]
Derivative assets	$ 50	$ 20
Rate lock commitments | Origination pull-through rate | Lower range
Fair Value Inputs, Assets and Liabilities, Quantitative Information [Line Items]
Rate lock commitment, fair value input	0.789	0.750
Rate lock commitments | Origination pull-through rate | Upper range
Fair Value Inputs, Assets and Liabilities, Quantitative Information [Line Items]
Rate lock commitment, fair value input	0.872	0.872
Rate lock commitments | Origination pull-through rate | Weighted Average
Fair Value Inputs, Assets and Liabilities, Quantitative Information [Line Items]
Rate lock commitment, fair value input	0.812	0.768
DOJ Liability
Fair Value Inputs, Assets and Liabilities, Quantitative Information [Line Items]
DOJ Liability	$ (35)	$ (60)
Contingent consideration
Fair Value Inputs, Assets and Liabilities, Quantitative Information [Line Items]
Contingent consideration	$ (7)	$ (6)
Contingent consideration | Beta | Lower range
Fair Value Inputs, Assets and Liabilities, Quantitative Information [Line Items]
Fair value inputs, equity volatility	0.6	0.6
Contingent consideration | Beta | Upper range
Fair Value Inputs, Assets and Liabilities, Quantitative Information [Line Items]
Fair value inputs, equity volatility	1.6	1.6
Contingent consideration | Beta | Weighted Average
Fair Value Inputs, Assets and Liabilities, Quantitative Information [Line Items]
Fair value inputs, equity volatility	1.1	1.1
Contingent consideration | Equity volatility | Lower range
Fair Value Inputs, Assets and Liabilities, Quantitative Information [Line Items]
Fair value inputs, equity volatility	0.266	0.266
Contingent consideration | Equity volatility | Upper range
Fair Value Inputs, Assets and Liabilities, Quantitative Information [Line Items]
Fair value inputs, equity volatility	0.589	0.589
Contingent consideration | Equity volatility | Weighted Average
Fair Value Inputs, Assets and Liabilities, Quantitative Information [Line Items]
Fair value inputs, equity volatility	0.400	0.400