Investments - Analysis of Cost or Amortized Cost, Gross Unrealized Gains and Losses and Fair Value for Investments (Detail) - Debt Securities - USD ($) $ in Millions	Jun. 30, 2021	Dec. 31, 2020
Debt Securities, Available-for-sale
Cost or Amortized Cost	$ 11,827	$ 11,312
Available-for-sale Securities, Accumulated Gross Unrealized Gain, before Tax	966	1,036
Available-for-sale Securities, Accumulated Gross Unrealized Loss, before Tax	4	10
Fair Value	12,789	12,338
Corporate
Debt Securities, Available-for-sale
Cost or Amortized Cost	6,775	6,281
Available-for-sale Securities, Accumulated Gross Unrealized Gain, before Tax	581	621
Available-for-sale Securities, Accumulated Gross Unrealized Loss, before Tax	2	7
Fair Value	7,354	6,895
States, municipalities and political subdivisions
Debt Securities, Available-for-sale
Cost or Amortized Cost	4,632	4,604
Available-for-sale Securities, Accumulated Gross Unrealized Gain, before Tax	367	395
Available-for-sale Securities, Accumulated Gross Unrealized Loss, before Tax	2	2
Fair Value	4,997	4,997
Commercial mortgage-backed
Debt Securities, Available-for-sale
Cost or Amortized Cost	268	271
Available-for-sale Securities, Accumulated Gross Unrealized Gain, before Tax	14	15
Available-for-sale Securities, Accumulated Gross Unrealized Loss, before Tax	0	1
Fair Value	282	285
United States government
Debt Securities, Available-for-sale
Cost or Amortized Cost	122	115
Available-for-sale Securities, Accumulated Gross Unrealized Gain, before Tax	4	5
Available-for-sale Securities, Accumulated Gross Unrealized Loss, before Tax	0	0
Fair Value	126	120
Foreign government
Debt Securities, Available-for-sale
Cost or Amortized Cost	23	29
Available-for-sale Securities, Accumulated Gross Unrealized Gain, before Tax	0	0
Available-for-sale Securities, Accumulated Gross Unrealized Loss, before Tax	0	0
Fair Value	23	29
Government-sponsored enterprises
Debt Securities, Available-for-sale
Cost or Amortized Cost	7	12
Available-for-sale Securities, Accumulated Gross Unrealized Gain, before Tax	0	0
Available-for-sale Securities, Accumulated Gross Unrealized Loss, before Tax	0	0
Fair Value	$ 7	$ 12

Amount of investment in debt and equity securities categorized neither as held-to-maturity nor trading.

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- Definition

Amount before tax of unrealized gain in accumulated other comprehensive income (AOCI) on investments in debt and equity securities classified as available-for-sale.

+ References

Reference 1: http://fasb.org/us-gaap/role/ref/legacyRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 320
-SubTopic 10
-Section 50
-Paragraph 2
-Subparagraph (b)
-URI http://asc.fasb.org/extlink&oid=123581744&loc=d3e27161-111563

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- Definition

Amount before tax of unrealized loss in accumulated other comprehensive income (AOCI) on investments in debt and equity securities classified as available-for-sale.

+ References

No definition available.

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This item represents the cost of debt and equity securities, which are categorized neither as held-to-maturity nor trading, net of adjustments including accretion, amortization, collection of cash, previous other-than-temporary impairments recognized in earnings (less any cumulative-effect adjustments recognized, as defined), and fair value hedge accounting adjustments, if any.

+ References

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- Definition

Line items represent financial concepts included in a table. These concepts are used to disclose reportable information associated with domain members defined in one or many axes to the table.

+ References

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