Premiums Receivable - Rollforward of Premiums Receivable and Agents' Balances (Details) - USD ($) $ in Millions	3 Months Ended
Mar. 31, 2020	Jan. 01, 2020
Premium Receivable, Allowance for Credit Loss [Roll Forward]
Premium Receivable, Allowance for Credit Loss	$ (145)
Premium Receivable, Credit Loss Expense (Reversal)	(30)
Premium Receivable, Allowance for Credit Loss, Writeoff	15
Premium Receivable, Allowance for Credit Loss, Recovery	(2)
Premium Receivable, Allowance for Credit Loss	(139)
Accounting Standards Update 2016-13 [Member]
Premium Receivable, Allowance for Credit Loss [Roll Forward]
New Accounting Pronouncement or Change in Accounting Principle, Cumulative Effect of Change on Equity or Net Assets		$ (2)
Accounting Standards Update 2016-13 [Member] \| Premiums Receivable [Member]
Premium Receivable, Allowance for Credit Loss [Roll Forward]
New Accounting Pronouncement or Change in Accounting Principle, Cumulative Effect of Change on Equity or Net Assets		23
Premiums Receivable, Due in One Year or Less, Excluding Receivables for Loss within a Deductible and Retrospectively-Rated Policy Premiums [Member]
Premium Receivable, Allowance for Credit Loss [Roll Forward]
Premium Receivable, Allowance for Credit Loss	(85)
Premium Receivable, Credit Loss Expense (Reversal)	(28)
Premium Receivable, Allowance for Credit Loss, Writeoff	15
Premium Receivable, Allowance for Credit Loss, Recovery	(2)
Premium Receivable, Allowance for Credit Loss	(98)
Premiums Receivable, Due in One Year or Less, Excluding Receivables for Loss within a Deductible and Retrospectively-Rated Policy Premiums [Member] \| Accounting Standards Update 2016-13 [Member] \| Premiums Receivable [Member]
Premium Receivable, Allowance for Credit Loss [Roll Forward]
New Accounting Pronouncement or Change in Accounting Principle, Cumulative Effect of Change on Equity or Net Assets		2
Premiums Receivable, Loss Within a Deductible and Retrospectively-Rated Policy Premiums [Member]
Premium Receivable, Allowance for Credit Loss [Roll Forward]
Premium Receivable, Allowance for Credit Loss	(60)
Premium Receivable, Credit Loss Expense (Reversal)	(2)
Premium Receivable, Allowance for Credit Loss, Writeoff	0
Premium Receivable, Allowance for Credit Loss, Recovery	0
Premium Receivable, Allowance for Credit Loss	$ (41)
Premiums Receivable, Loss Within a Deductible and Retrospectively-Rated Policy Premiums [Member] \| Accounting Standards Update 2016-13 [Member] \| Premiums Receivable [Member]
Premium Receivable, Allowance for Credit Loss [Roll Forward]
New Accounting Pronouncement or Change in Accounting Principle, Cumulative Effect of Change on Equity or Net Assets		$ 21

Amount of cumulative effect of the change in accounting principle or new accounting pronouncement on retained earnings or other components of equity or net assets in the statement of financial position as of the beginning of the earliest period presented.

Reference 1: http://fasb.org/us-gaap/role/ref/legacyRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 250
-SubTopic 10
-Section 50
-Paragraph 1
-Subparagraph (b)(3)
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- Definition

Amount of expense (reversal of expense) for expected credit loss on premium receivable.

+ References

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- Definition

The carrying value as of the balance sheet date of the estimated valuation allowance to reduce gross premiums receivable to net realizable value.

+ References

Reference 1: http://www.xbrl.org/2003/role/disclosureRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 944
-SubTopic 210
-Section S99
-Paragraph 1
-Subparagraph (SX 210.7-03(5))
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Reference 2: http://www.xbrl.org/2009/role/commonPracticeRef
-Publisher FASB
-Name Accounting Standards Codification
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Reference 3: http://www.xbrl.org/2009/role/commonPracticeRef
-Publisher FASB
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-Publisher FASB
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- Definition

Amount of recoveries of premiums receivable that were previously written off as bad debts.

+ References

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- Definition

A roll forward is a reconciliation of a concept from the beginning of a period to the end of a period.

+ References

No definition available.

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- Definition

Amount of writeoff of premium receivable, charged against allowance for credit loss.

+ References

Reference 1: http://www.xbrl.org/2009/role/commonPracticeRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 326
-SubTopic 20
-Section 50
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-URI http://asc.fasb.org/extlink&oid=119407570&loc=SL82919249-210447

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