Fair Value Measurements - Quantitative Information about Recurring Level 3 Fair Value Instruments (Details) - Level 3 - Fair Value $ in Millions	Sep. 30, 2020 USD ($) constantPrepaymentRatePerLoan constant_default_rate_per_loan orginationPull-throughRatePerLoan $ / loan discountRatePerLoan optionAdjustedSpreadPerLoan	Dec. 31, 2019 USD ($) optionAdjustedSpreadPerLoan orginationPull-throughRatePerLoan constantPrepaymentRatePerLoan constant_default_rate_per_loan $ / loan discountRatePerLoan
Home equity
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Loans held-for-investment | $	$ 2	$ 2
Home equity | Discount rate | Lower range
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Loans held for investment, fair value input (in percentage) | discountRatePerLoan	0.072	0.072
Home equity | Discount rate | Upper range
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Loans held for investment, fair value input (in percentage) | discountRatePerLoan	0.108	0.108
Home equity | Discount rate | Weighted average
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Loans held for investment, fair value input (in percentage) | discountRatePerLoan	0.090	0.090
Home equity | Constant prepayment rate | Lower range
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Loans held for investment, fair value input (in percentage) | constantPrepaymentRatePerLoan	0.231	0.130
Home equity | Constant prepayment rate | Upper range
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Loans held for investment, fair value input (in percentage) | constantPrepaymentRatePerLoan	0.347	0.195
Home equity | Constant prepayment rate | Weighted average
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Loans held for investment, fair value input (in percentage) | constantPrepaymentRatePerLoan	0.289	0.162
Home equity | Constant default rate | Lower range
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Loans held for investment, fair value input (in percentage) | constant_default_rate_per_loan	0.017	0.027
Home equity | Constant default rate | Upper range
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Loans held for investment, fair value input (in percentage) | constant_default_rate_per_loan	0.026	0.040
Home equity | Constant default rate | Weighted average
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Loans held for investment, fair value input (in percentage) | constant_default_rate_per_loan	0.022	0.033
Mortgage servicing rights
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Servicing asset | $	$ 323	$ 291
Mortgage servicing rights | Constant prepayment rate | Lower range
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Servicing asset, measurement input | constantPrepaymentRatePerLoan	0	0
Mortgage servicing rights | Constant prepayment rate | Upper range
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Servicing asset, measurement input | constantPrepaymentRatePerLoan	0.143	0.123
Mortgage servicing rights | Constant prepayment rate | Weighted average
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Servicing asset, measurement input | constantPrepaymentRatePerLoan	0.114	0.106
Mortgage servicing rights | Option adjusted spread | Lower range
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Servicing asset, measurement input | optionAdjustedSpreadPerLoan	0.037	0.024
Mortgage servicing rights | Option adjusted spread | Upper range
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Servicing asset, measurement input | optionAdjustedSpreadPerLoan	0.212	0.204
Mortgage servicing rights | Option adjusted spread | Weighted average
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Servicing asset, measurement input | optionAdjustedSpreadPerLoan	0.076	0.053
Mortgage servicing rights | Weighted average cost to service per loan | Lower range
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Servicing asset, measurement input | $ / loan	67	67
Mortgage servicing rights | Weighted average cost to service per loan | Upper range
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Servicing asset, measurement input | $ / loan	95	95
Mortgage servicing rights | Weighted average cost to service per loan | Weighted average
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Servicing asset, measurement input | $ / loan	82	84
Rate lock commitments (net)
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Derivative asset | $	$ 257	$ 34
Rate lock commitments (net) | Closing pull-through rate | Lower range
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Derivative asset, measurement input (in percentage) | orginationPull-throughRatePerLoan	0.806
Rate lock commitments (net) | Closing pull-through rate | Upper range
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Derivative asset, measurement input (in percentage) | orginationPull-throughRatePerLoan	0.872
Rate lock commitments (net) | Closing pull-through rate | Weighted average
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Derivative asset, measurement input (in percentage) | orginationPull-throughRatePerLoan	0.819
Rate lock commitments (net) | Origination pull-through rate | Lower range
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Derivative asset, measurement input (in percentage) | orginationPull-throughRatePerLoan		0.800
Rate lock commitments (net) | Origination pull-through rate | Upper range
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Derivative asset, measurement input (in percentage) | orginationPull-throughRatePerLoan		0.872
Rate lock commitments (net) | Origination pull-through rate | Weighted average
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Derivative asset, measurement input (in percentage) | orginationPull-throughRatePerLoan		0.815
DOJ Liability
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Litigation settlement at fair value | $	$ (35)	$ (35)
Contingent consideration
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Contingent consideration | $		$ (10)