Fair Value Measurements - Assets and Liabilities Measured at Fair Value on a Recurring Basis (Details) - USD ($) $ in Millions	Sep. 30, 2022	Dec. 31, 2021
Assets
Investment securities available-for-sale	$ 2,627.0	$ 1,804.0
Loans held-for-sale	1,822.0	4,920.0
Loans held-for-investment	24.0	16.0
Mortgage servicing rights	1,026.0	392.0
Total assets at fair value	1,846.0	4,936.0
Agency - Commercial
Assets
Investment securities available-for-sale	1,840.0	747.0
Agency - Residential
Assets
Investment securities available-for-sale	507.0	696.0
Municipal obligations
Assets
Investment securities available-for-sale	14.0	20.0
Corporate debt obligations
Assets
Investment securities available-for-sale	58.0	73.0
Certificate of deposit
Assets
Investment securities available-for-sale	1.0	1.0
Estimate of Fair Value Measurement
Assets
Investment securities available-for-sale	2,627.0	1,804.0
Loans held-for-sale	1,830.0	5,054.0
Loans held-for-investment	15,364.0	13,453.0
Mortgage servicing rights	1,026.0	392.0
Level 1 \| Estimate of Fair Value Measurement
Assets
Investment securities available-for-sale	0.0	0.0
Loans held-for-sale	0.0	0.0
Loans held-for-investment	0.0	0.0
Mortgage servicing rights	0.0	0.0
Level 2 \| Estimate of Fair Value Measurement
Assets
Investment securities available-for-sale	2,627.0	1,804.0
Loans held-for-sale	1,830.0	5,054.0
Loans held-for-investment	23.0	14.0
Mortgage servicing rights	0.0	0.0
Level 3 \| Estimate of Fair Value Measurement
Assets
Investment securities available-for-sale	0.0	0.0
Loans held-for-sale	0.0	0.0
Loans held-for-investment	15,341.0	13,439.0
Mortgage servicing rights	1,026.0	392.0
Recurring \| Estimate of Fair Value Measurement
Assets
Mortgage servicing rights	1,026.0	392.0
Total assets at fair value	5,853.0	7,273.0
Liabilities
Total liabilities at fair value	(122.0)	(20.0)
Recurring \| Estimate of Fair Value Measurement \| Rate lock commitments
Assets
Derivative assets	10.0	54.0
Liabilities
Derivative liabilities	(29.0)	(1.0)
Recurring \| Estimate of Fair Value Measurement \| Futures
Assets
Derivative assets	3.0
Recurring \| Estimate of Fair Value Measurement \| Mortgage-backed securities forwards
Assets
Derivative assets	162.0	10.0
Liabilities
Derivative liabilities	(22.0)	(14.0)
Recurring \| Estimate of Fair Value Measurement \| Interest rate swaps and swaptions
Assets
Derivative assets	179.0	77.0
Liabilities
Derivative liabilities		(5.0)
Recurring \| Estimate of Fair Value Measurement \| Interest rate swaps
Liabilities
Derivative liabilities	(71.0)
Recurring \| Estimate of Fair Value Measurement \| Residential first mortgage loans
Assets
Loans held-for-sale	1,822.0	4,920.0
Loans held-for-investment	24.0	15.0
Recurring \| Estimate of Fair Value Measurement \| Home equity
Assets
Loans held-for-investment		1.0
Recurring \| Estimate of Fair Value Measurement \| Agency - Commercial
Assets
Investment securities available-for-sale	1,840.0	747.0
Recurring \| Estimate of Fair Value Measurement \| Agency - Residential
Assets
Investment securities available-for-sale	507.0	696.0
Recurring \| Estimate of Fair Value Measurement \| Municipal obligations
Assets
Investment securities available-for-sale	14.0	20.0
Recurring \| Estimate of Fair Value Measurement \| Corporate debt obligations
Assets
Investment securities available-for-sale	58.0	73.0
Recurring \| Estimate of Fair Value Measurement \| Other MBS
Assets
Investment securities available-for-sale	207.0	267.0
Recurring \| Estimate of Fair Value Measurement \| Certificate of deposit
Assets
Investment securities available-for-sale	1.0	1.0
Recurring \| Level 1
Assets
Mortgage servicing rights	0.0	0.0
Total assets at fair value	0.0	0.0
Liabilities
Total liabilities at fair value	0.0	0.0
Recurring \| Level 1 \| Rate lock commitments
Assets
Derivative assets	0.0	0.0
Liabilities
Derivative liabilities	0.0	0.0
Recurring \| Level 1 \| Futures
Assets
Derivative assets	0.0
Recurring \| Level 1 \| Mortgage-backed securities forwards
Assets
Derivative assets	0.0	0.0
Liabilities
Derivative liabilities	0.0	0.0
Recurring \| Level 1 \| Interest rate swaps and swaptions
Assets
Derivative assets	0.0	0.0
Liabilities
Derivative liabilities		0.0
Recurring \| Level 1 \| Interest rate swaps
Liabilities
Derivative liabilities	0.0
Recurring \| Level 1 \| Residential first mortgage loans
Assets
Loans held-for-sale	0.0	0.0
Loans held-for-investment	0.0	0.0
Recurring \| Level 1 \| Home equity
Assets
Loans held-for-investment		0.0
Recurring \| Level 1 \| Agency - Commercial
Assets
Investment securities available-for-sale	0.0	0.0
Recurring \| Level 1 \| Agency - Residential
Assets
Investment securities available-for-sale	0.0	0.0
Recurring \| Level 1 \| Municipal obligations
Assets
Investment securities available-for-sale	0.0	0.0
Recurring \| Level 1 \| Corporate debt obligations
Assets
Investment securities available-for-sale	0.0	0.0
Recurring \| Level 1 \| Other MBS
Assets
Investment securities available-for-sale	0.0	0.0
Recurring \| Level 1 \| Certificate of deposit
Assets
Investment securities available-for-sale	0.0	0.0
Recurring \| Level 2
Assets
Mortgage servicing rights	0.0	0.0
Total assets at fair value	4,817.0	6,826.0
Liabilities
Total liabilities at fair value	(93.0)	(19.0)
Recurring \| Level 2 \| Rate lock commitments
Assets
Derivative assets	0.0	0.0
Liabilities
Derivative liabilities	0.0	0.0
Recurring \| Level 2 \| Futures
Assets
Derivative assets	3.0
Recurring \| Level 2 \| Mortgage-backed securities forwards
Assets
Derivative assets	162.0	10.0
Liabilities
Derivative liabilities	(22.0)	(14.0)
Recurring \| Level 2 \| Interest rate swaps and swaptions
Assets
Derivative assets	179.0	77.0
Liabilities
Derivative liabilities		(5.0)
Recurring \| Level 2 \| Interest rate swaps
Liabilities
Derivative liabilities	(71.0)
Recurring \| Level 2 \| Residential first mortgage loans
Assets
Loans held-for-sale	1,822.0	4,920.0
Loans held-for-investment	24.0	15.0
Recurring \| Level 2 \| Home equity
Assets
Loans held-for-investment		0.0
Recurring \| Level 2 \| Agency - Commercial
Assets
Investment securities available-for-sale	1,840.0	747.0
Recurring \| Level 2 \| Agency - Residential
Assets
Investment securities available-for-sale	507.0	696.0
Recurring \| Level 2 \| Municipal obligations
Assets
Investment securities available-for-sale	14.0	20.0
Recurring \| Level 2 \| Corporate debt obligations
Assets
Investment securities available-for-sale	58.0	73.0
Recurring \| Level 2 \| Other MBS
Assets
Investment securities available-for-sale	207.0	267.0
Recurring \| Level 2 \| Certificate of deposit
Assets
Investment securities available-for-sale	1.0	1.0
Recurring \| Level 3
Assets
Mortgage servicing rights	1,026.0	392.0
Total assets at fair value	1,036.0	447.0
Liabilities
Total liabilities at fair value	(29.0)	(1.0)
Recurring \| Level 3 \| Rate lock commitments
Assets
Derivative assets	10.0	54.0
Liabilities
Derivative liabilities	(29.0)	(1.0)
Recurring \| Level 3 \| Futures
Assets
Derivative assets	0.0
Recurring \| Level 3 \| Mortgage-backed securities forwards
Assets
Derivative assets	0.0	0.0
Liabilities
Derivative liabilities	0.0	0.0
Recurring \| Level 3 \| Interest rate swaps and swaptions
Assets
Derivative assets	0.0	0.0
Liabilities
Derivative liabilities		0.0
Recurring \| Level 3 \| Interest rate swaps
Liabilities
Derivative liabilities	0.0
Recurring \| Level 3 \| Residential first mortgage loans
Assets
Loans held-for-sale	0.0	0.0
Loans held-for-investment	0.0	0.0
Recurring \| Level 3 \| Home equity
Assets
Loans held-for-investment		1.0
Recurring \| Level 3 \| Agency - Commercial
Assets
Investment securities available-for-sale	0.0	0.0
Recurring \| Level 3 \| Agency - Residential
Assets
Investment securities available-for-sale	0.0	0.0
Recurring \| Level 3 \| Municipal obligations
Assets
Investment securities available-for-sale	0.0	0.0
Recurring \| Level 3 \| Corporate debt obligations
Assets
Investment securities available-for-sale	0.0	0.0
Recurring \| Level 3 \| Other MBS
Assets
Investment securities available-for-sale	0.0	0.0
Recurring \| Level 3 \| Certificate of deposit
Assets
Investment securities available-for-sale	$ 0.0	$ 0.0

Fair value portion of probable future economic benefits obtained or controlled by an entity as a result of past transactions or events.

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Amount of investment in debt security measured at fair value with change in fair value recognized in other comprehensive income (available-for-sale).

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