Fair Value - Level 3 Unobservable Inputs, Mortgage Servicing Rights - Initial Recognition (Details)	12 Months Ended
	Dec. 31, 2021 USD ($) item	Dec. 31, 2020 USD ($) item	Dec. 31, 2019 USD ($) item
Mortgage servicing rights
Inputs
Amount recognized | $	$ 1,861,949,000	$ 1,138,045,000	$ 884,876,000
Total | Mortgage servicing rights | Level 3 | Minimum
Inputs:
Annual per-loan cost of servicing | $	79	79
Total | Mortgage servicing rights | Level 3 | Maximum
Inputs:
Annual per-loan cost of servicing | $	197	117
Total | Mortgage servicing rights | Level 3 | Weighted average
Inputs:
Annual per-loan cost of servicing | $	$ 108	$ 107
Total | Mortgage servicing rights | Pricing spread | Level 3 | Minimum
Inputs:
Input	5.3	8.0
Total | Mortgage servicing rights | Pricing spread | Level 3 | Maximum
Inputs:
Input	15.5	17.6
Total | Mortgage servicing rights | Pricing spread | Level 3 | Weighted average
Inputs:
Input	7.7	10.1
Total | Mortgage servicing rights | Annual total prepayment speed | Level 3 | Minimum
Inputs:
Input	7.9	10.1
Total | Mortgage servicing rights | Annual total prepayment speed | Level 3 | Maximum
Inputs:
Input	26.7	32.9
Total | Mortgage servicing rights | Annual total prepayment speed | Level 3 | Weighted average
Inputs:
Input	10.7	13.7
Total | Mortgage servicing rights | Life | Level 3 | Minimum
Inputs:
Input	3.1	2.3
Total | Mortgage servicing rights | Life | Level 3 | Maximum
Inputs:
Input	7.7	7.7
Total | Mortgage servicing rights | Life | Level 3 | Weighted average
Inputs:
Input	6.8	6.0
Total | Mortgage servicing rights | MSRs at the time of initial recognition, excluding MSR purchases | Level 3
Inputs
Amount recognized | $	$ 1,861,949,000	$ 1,138,045,000	884,876,000
Unpaid principal balance of underlying loans | $	$ 138,319,425,000	$ 96,571,835,000	$ 56,038,354,000
Weighted-average servicing fee rate (as a percent)	0.34%	0.35%	0.41%
Total | Mortgage servicing rights | MSRs at the time of initial recognition, excluding MSR purchases | Level 3 | Minimum
Inputs:
Annual per-loan cost of servicing | $	$ 80	$ 77	$ 78
Total | Mortgage servicing rights | MSRs at the time of initial recognition, excluding MSR purchases | Level 3 | Maximum
Inputs:
Annual per-loan cost of servicing | $	117	117	100
Total | Mortgage servicing rights | MSRs at the time of initial recognition, excluding MSR purchases | Level 3 | Weighted average
Inputs:
Annual per-loan cost of servicing | $	$ 103	$ 102	$ 97
Total | Mortgage servicing rights | MSRs at the time of initial recognition, excluding MSR purchases | Pricing spread | Level 3 | Minimum
Inputs:
Input	6.0	6.8	5.5
Total | Mortgage servicing rights | MSRs at the time of initial recognition, excluding MSR purchases | Pricing spread | Level 3 | Maximum
Inputs:
Input	16.9	18.1	16.2
Total | Mortgage servicing rights | MSRs at the time of initial recognition, excluding MSR purchases | Pricing spread | Level 3 | Weighted average
Inputs:
Input	8.8	9.4	8.5
Total | Mortgage servicing rights | MSRs at the time of initial recognition, excluding MSR purchases | Annual total prepayment speed | Level 3 | Minimum
Inputs:
Input	6.1	7.2	7.7
Total | Mortgage servicing rights | MSRs at the time of initial recognition, excluding MSR purchases | Annual total prepayment speed | Level 3 | Maximum
Inputs:
Input	31.4	49.8	32.8
Total | Mortgage servicing rights | MSRs at the time of initial recognition, excluding MSR purchases | Annual total prepayment speed | Level 3 | Weighted average
Inputs:
Input	8.6	11.9	13.5
Total | Mortgage servicing rights | MSRs at the time of initial recognition, excluding MSR purchases | Life | Level 3 | Minimum
Inputs:
Input	3.0	1.5	2.6
Total | Mortgage servicing rights | MSRs at the time of initial recognition, excluding MSR purchases | Life | Level 3 | Maximum
Inputs:
Input	9.2	9.1	8.2
Total | Mortgage servicing rights | MSRs at the time of initial recognition, excluding MSR purchases | Life | Level 3 | Weighted average
Inputs:
Input	8.1	6.7	6.2