Investments - Analysis of Cost or Amortized Cost, Gross Unrealized Gains and Losses and Fair Value for Investments (Detail) - Debt Securities - USD ($) $ in Millions	Mar. 31, 2020	Dec. 31, 2019
Debt Securities, Available-for-sale
Cost or Amortized Cost	$ 11,074	$ 11,108
Available-for-sale Securities, Accumulated Gross Unrealized Gain, before Tax	461	597
Available-for-sale Securities, Accumulated Gross Unrealized Loss, before Tax	195	7
Fair Value	11,340	11,698
Corporate
Debt Securities, Available-for-sale
Cost or Amortized Cost	6,134	6,074
Available-for-sale Securities, Accumulated Gross Unrealized Gain, before Tax	180	332
Available-for-sale Securities, Accumulated Gross Unrealized Loss, before Tax	181	5
Fair Value	6,133	6,401
States, municipalities and political subdivisions
Debt Securities, Available-for-sale
Cost or Amortized Cost	4,445	4,477
Available-for-sale Securities, Accumulated Gross Unrealized Gain, before Tax	272	252
Available-for-sale Securities, Accumulated Gross Unrealized Loss, before Tax	6	1
Fair Value	4,711	4,728
Commercial mortgage-backed
Debt Securities, Available-for-sale
Cost or Amortized Cost	290	290
Available-for-sale Securities, Accumulated Gross Unrealized Gain, before Tax	2	11
Available-for-sale Securities, Accumulated Gross Unrealized Loss, before Tax	8	0
Fair Value	284	301
United States government
Debt Securities, Available-for-sale
Cost or Amortized Cost	96	102
Available-for-sale Securities, Accumulated Gross Unrealized Gain, before Tax	6	2
Available-for-sale Securities, Accumulated Gross Unrealized Loss, before Tax	0	0
Fair Value	102	104
Government-sponsored enterprises
Debt Securities, Available-for-sale
Cost or Amortized Cost	86	137
Available-for-sale Securities, Accumulated Gross Unrealized Gain, before Tax	1	0
Available-for-sale Securities, Accumulated Gross Unrealized Loss, before Tax	0	1
Fair Value	87	136
Foreign government
Debt Securities, Available-for-sale
Cost or Amortized Cost	23	28
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	$ 28

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

No definition available.

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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=118939692&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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- Definition

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

No definition available.

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