Allowance for Credit Losses (Summary of Activity in the Allowance for Credit Losses by Loan Portfolio) (Details) - USD ($) $ in Thousands		12 Months Ended
Nov. 15, 2021	Dec. 31, 2022	Dec. 31, 2021
Financing Receivable, Allowance for Credit Loss [Roll Forward]
Allowance for credit losses at beginning of period		$ 299,653	$ 379,910
Other adjustments		(108)	3
Charge-offs		(31,779)	(35,019)
Recoveries		11,503	13,569
Provision for credit losses		78,179	(59,280)
Allowance for credit losses at period end		357,448	299,653
Individually evaluated for impairment		6,799	8,552
Collectively evaluated for impairment		350,649	291,101
Loans at period end, individually evaluated for impairment		90,197	93,270
Loans at period end, collectively evaluated for impairment		38,926,356	34,657,236
Loans held-for-investment		179,932	38,598
Allstate Corporation Loan Portfolio
Financing Receivable, Allowance for Credit Loss [Roll Forward]
Initial allowance for credit losses recognized on PCD assets acquired during period			470
Allowance for credit losses	$ 2,800
Allowance for credit losses, amounts charged-off	$ 2,300
Allstate Corporation Loan Portfolio \| Loans acquired with deteriorated credit quality
Financing Receivable, Allowance for Credit Loss [Roll Forward]
Initial allowance for credit losses recognized on PCD assets acquired during period			470
Commercial
Financing Receivable, Allowance for Credit Loss [Roll Forward]
Allowance for credit losses at beginning of period		119,307	94,212
Other adjustments		0	0
Charge-offs		(14,141)	(20,801)
Recoveries		4,748	2,559
Provision for credit losses		32,855	42,867
Allowance for credit losses at period end		142,769	119,307
Individually evaluated for impairment		5,973	5,196
Collectively evaluated for impairment		136,796	114,111
Loans at period end, individually evaluated for impairment		38,042	24,530
Loans at period end, collectively evaluated for impairment		12,511,122	11,879,538
Loans held-for-investment		0	0
Commercial \| Allstate Corporation Loan Portfolio \| Loans acquired with deteriorated credit quality
Financing Receivable, Allowance for Credit Loss [Roll Forward]
Initial allowance for credit losses recognized on PCD assets acquired during period			470
Commercial Real Estate
Financing Receivable, Allowance for Credit Loss [Roll Forward]
Allowance for credit losses at beginning of period		144,583	243,603
Other adjustments		0	0
Charge-offs		(1,379)	(3,293)
Recoveries		701	1,304
Provision for credit losses		40,447	(97,031)
Allowance for credit losses at period end		184,352	144,583
Individually evaluated for impairment		61	2,237
Collectively evaluated for impairment		184,291	142,346
Loans at period end, individually evaluated for impairment		21,435	30,167
Loans at period end, collectively evaluated for impairment		9,929,512	8,960,119
Loans held-for-investment		0	0
Commercial Real Estate \| Allstate Corporation Loan Portfolio \| Loans acquired with deteriorated credit quality
Financing Receivable, Allowance for Credit Loss [Roll Forward]
Initial allowance for credit losses recognized on PCD assets acquired during period			0
Home Equity
Financing Receivable, Allowance for Credit Loss [Roll Forward]
Allowance for credit losses at beginning of period		10,699	11,437
Other adjustments		0	0
Charge-offs		(432)	(336)
Recoveries		319	1,203
Provision for credit losses		(3,013)	(1,605)
Allowance for credit losses at period end		7,573	10,699
Individually evaluated for impairment		50	192
Collectively evaluated for impairment		7,523	10,507
Loans at period end, individually evaluated for impairment		10,351	14,656
Loans at period end, collectively evaluated for impairment		322,347	320,499
Loans held-for-investment		0	0
Home Equity \| Allstate Corporation Loan Portfolio \| Loans acquired with deteriorated credit quality
Financing Receivable, Allowance for Credit Loss [Roll Forward]
Initial allowance for credit losses recognized on PCD assets acquired during period			0
Residential Real Estate
Financing Receivable, Allowance for Credit Loss [Roll Forward]
Allowance for credit losses at beginning of period		8,782	12,459
Other adjustments		0	0
Charge-offs		(471)	(1,082)
Recoveries		77	330
Provision for credit losses		3,197	(2,925)
Allowance for credit losses at period end		11,585	8,782
Individually evaluated for impairment		715	899
Collectively evaluated for impairment		10,870	7,883
Loans at period end, individually evaluated for impairment		20,300	23,306
Loans at period end, collectively evaluated for impairment		2,172,151	1,575,195
Loans held-for-investment		179,932	38,598
Residential Real Estate \| Allstate Corporation Loan Portfolio \| Loans acquired with deteriorated credit quality
Financing Receivable, Allowance for Credit Loss [Roll Forward]
Initial allowance for credit losses recognized on PCD assets acquired during period			0
Premium Finance Receivable
Financing Receivable, Allowance for Credit Loss [Roll Forward]
Allowance for credit losses at beginning of period		15,859	17,777
Other adjustments		(108)	3
Charge-offs		(14,275)	(9,020)
Recoveries		5,522	7,989
Provision for credit losses		3,673	(890)
Allowance for credit losses at period end		10,671	15,859
Individually evaluated for impairment		0	0
Collectively evaluated for impairment		10,671	15,859
Loans at period end, individually evaluated for impairment		0	0
Loans at period end, collectively evaluated for impairment		13,940,457	11,898,297
Loans held-for-investment		0	0
Premium Finance Receivable \| Allstate Corporation Loan Portfolio \| Loans acquired with deteriorated credit quality
Financing Receivable, Allowance for Credit Loss [Roll Forward]
Initial allowance for credit losses recognized on PCD assets acquired during period			0
Consumer and other
Financing Receivable, Allowance for Credit Loss [Roll Forward]
Allowance for credit losses at beginning of period		423	422
Other adjustments		0	0
Charge-offs		(1,081)	(487)
Recoveries		136	184
Provision for credit losses		1,020	304
Allowance for credit losses at period end		498	423
Individually evaluated for impairment		0	28
Collectively evaluated for impairment		498	395
Loans at period end, individually evaluated for impairment		69	611
Loans at period end, collectively evaluated for impairment		50,767	23,588
Loans held-for-investment		$ 0	0
Consumer and other \| Allstate Corporation Loan Portfolio \| Loans acquired with deteriorated credit quality
Financing Receivable, Allowance for Credit Loss [Roll Forward]
Initial allowance for credit losses recognized on PCD assets acquired during period			$ 0

Reserve for loans impairments recorded after acquisition as a result of current information and events which result in it being probable that estimated cash flows will be less than previously expected or because actual cash flows are less than cash flows previously expected. This relates to loans not accounted for as debt securities, with evidence of deterioration of credit quality since origination that was acquired by completion of a transfer for which it is probable, at acquisition, that the investor will be unable to collect all contractually required payments receivable.

Reference 1: http://fasb.org/us-gaap/role/ref/legacyRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 310
-SubTopic 30
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Amount of reduction in the reserve for loans impairments as a result of current information and events which result in it being probable that estimated cash flows will be significantly higher than previously expected or because actual cash flows are significantly greater than cash flows previously expected for loans not accounted for as debt securities, with evidence of deterioration of credit quality since origination that was acquired by completion of a transfer for which it is probable, at acquisition, that the investor will be unable to collect all contractually required payments receivable.

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Amount excluding accrued interest, of allowance for credit loss on financing receivable. Excludes net investment in lease.

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The valuation allowance for financing receivables that are expected to be uncollectible that were collectively evaluated for impairment.

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Amount of valuation allowance for financing receivables that are expected to be uncollectible that were individually evaluated for impairment.

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The balance of financing receivables that were collectively evaluated for impairment.

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Amount, excluding accrued interest, of increase in allowance for credit loss on financing receivable from recovery. Excludes net investment in lease.

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Reference 1: http://www.xbrl.org/2003/role/disclosureRef
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Amount, excluding accrued interest, of decrease in allowance for credit loss on financing receivable from writeoff. Excludes net investment in lease.

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Amount, excluding accrued interest, of credit loss expense (reversal of expense) on financing receivable. Excludes net investment in lease.

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The balance of financing receivables that were individually evaluated for impairment.

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Certain Loans Acquired In Transfer Not Accounted For As Debt Securities, Allowance For Loan Losses, Net

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