Fair Value - Level 3 Unobservable Inputs, Mortgage Servicing Rights - Initial Recognition (Details)	3 Months Ended		6 Months Ended		12 Months Ended
	Jun. 30, 2021 USD ($) item	Jun. 30, 2020 USD ($) item	Jun. 30, 2021 USD ($) item	Jun. 30, 2020 USD ($) item	Dec. 31, 2020 USD ($) item
Mortgage servicing rights
Inputs
Amount recognized | $	$ 483,362,000	$ 225,534,000	$ 953,895,000	$ 507,849,000
Fair Values | Mortgage servicing rights | Level 3 | Minimum
Inputs:
Annual per-loan cost of servicing | $			79		$ 79
Fair Values | Mortgage servicing rights | Level 3 | Maximum
Inputs:
Annual per-loan cost of servicing | $			117		117
Fair Values | Mortgage servicing rights | Level 3 | Weighted average
Inputs:
Annual per-loan cost of servicing | $			$ 107		$ 107
Fair Values | Mortgage servicing rights | Pricing spread | Level 3 | Minimum
Inputs:
Input	6.3		6.3		8.0
Fair Values | Mortgage servicing rights | Pricing spread | Level 3 | Maximum
Inputs:
Input					17.6
Fair Values | Mortgage servicing rights | Pricing spread | Level 3 | Weighted average
Inputs:
Input	8.4		8.4		10.1
Fair Values | Mortgage servicing rights | Annual total prepayment speed | Level 3 | Minimum
Inputs:
Input	7.9		7.9		10.1
Fair Values | Mortgage servicing rights | Annual total prepayment speed | Level 3 | Maximum
Inputs:
Input	29.1		29.1		32.9
Fair Values | Mortgage servicing rights | Annual total prepayment speed | Level 3 | Weighted average
Inputs:
Input	10.5		10.5		13.7
Fair Values | Mortgage servicing rights | Life | Level 3 | Minimum
Inputs:
Input	3.0		3.0		2.3
Fair Values | Mortgage servicing rights | Life | Level 3 | Maximum
Inputs:
Input	7.8		7.8		7.7
Fair Values | Mortgage servicing rights | Life | Level 3 | Weighted average
Inputs:
Input	6.9		6.9		6.0
Fair Values | MSRs at the time of initial recognition, excluding MSR purchases | Level 3
Inputs
Amount recognized | $	$ 483,362,000	225,534,000	$ 953,895,000	507,849,000
Unpaid principal balance of underlying loans | $	$ 36,830,098,000	$ 20,066,302,000	$ 71,773,352,000	$ 38,396,686,000
Weighted-average servicing fee rate (as a percent)	0.33%	0.36%	0.33%	0.38%
Fair Values | MSRs at the time of initial recognition, excluding MSR purchases | Level 3 | Minimum
Inputs:
Annual per-loan cost of servicing | $	$ 80	$ 79		$ 77
Fair Values | MSRs at the time of initial recognition, excluding MSR purchases | Level 3 | Maximum
Inputs:
Annual per-loan cost of servicing | $	117	110	$ 117	110
Fair Values | MSRs at the time of initial recognition, excluding MSR purchases | Level 3 | Weighted average
Inputs:
Annual per-loan cost of servicing | $	$ 104	$ 101	$ 104	$ 99
Fair Values | MSRs at the time of initial recognition, excluding MSR purchases | Pricing spread | Level 3 | Minimum
Inputs:
Input	6.0	8.1	6.0	6.8
Fair Values | MSRs at the time of initial recognition, excluding MSR purchases | Pricing spread | Level 3 | Maximum
Inputs:
Input	16.9	18.1	16.9	18.1
Fair Values | MSRs at the time of initial recognition, excluding MSR purchases | Pricing spread | Level 3 | Weighted average
Inputs:
Input	8.9	9.9	9.2	9.1
Fair Values | MSRs at the time of initial recognition, excluding MSR purchases | Annual total prepayment speed | Level 3 | Minimum
Inputs:
Input	6.7	8.8	6.2	8.8
Fair Values | MSRs at the time of initial recognition, excluding MSR purchases | Annual total prepayment speed | Level 3 | Maximum
Inputs:
Input	17.7	29.1	16.7	49.8
Fair Values | MSRs at the time of initial recognition, excluding MSR purchases | Annual total prepayment speed | Level 3 | Weighted average
Inputs:
Input	8.5	13.0	8.1	13.7
Fair Values | MSRs at the time of initial recognition, excluding MSR purchases | Life | Level 3 | Minimum
Inputs:
Input	4.0	2.9	4.1	1.5
Fair Values | MSRs at the time of initial recognition, excluding MSR purchases | Life | Level 3 | Maximum
Inputs:
Input	8.8	8.1	9.0	8.1
Fair Values | MSRs at the time of initial recognition, excluding MSR purchases | Life | Level 3 | Weighted average
Inputs:
Input	8.1	6.3	8.3	6.1