Fair Value Measurements (Tables)

12 Months Ended

Dec. 31, 2023

Fair Value Disclosures [Abstract]

Level within the fair value hierarchy at which the Company's financial assets and financial liabilities are measured on a recurring basis [Table Text Block]

The following tables present the level within the fair value hierarchy at which the Company’s financial assets and financial liabilities are measured on a recurring basis.

(at December 31, 2023, in millions)	Total		Level 1		Level 2		Level 3
Invested assets:
Fixed maturities
U.S. Treasury securities and obligations of U.S. government and government agencies and authorities	$	6,368	$	6,368	$	—	$	—
Obligations of U.S. states, municipalities and political subdivisions	28,506		—		28,506		—
Debt securities issued by foreign governments	1,006		—		1,006		—
Mortgage-backed securities, collateralized mortgage obligations and pass-through securities	7,818		—		7,818		—
Corporate and all other bonds	34,109		—		33,851		258
Total fixed maturities	77,807		6,368		71,181		258
Equity securities
Common stock	560		553		—		7
Non-redeemable preferred stock	48		16		2		30
Total equity securities	608		569		2		37
Other investments	18		18		—		—
Total	$	78,433	$	6,955	$	71,183	$	295

(at December 31, 2022, in millions)	Total		Level 1		Level 2		Level 3
Invested assets:
Fixed maturities
U.S. Treasury securities and obligations of U.S. government and government agencies and authorities	$	5,438	$	5,438	$	—	$	—
Obligations of U.S. states, municipalities and political subdivisions	31,379		—		31,379		—
Debt securities issued by foreign governments	994		—		994		—
Mortgage-backed securities, collateralized mortgage obligations and pass-through securities	1,991		—		1,991		—
Corporate and all other bonds	31,358		—		31,055		303
Total fixed maturities	71,160		5,438		65,419		303
Equity securities
Common stock	763		418		—		345
Non-redeemable preferred stock	44		15		3		26
Total equity securities	807		433		3		371
Other investments	16		15		—		1
Total	$	71,983	$	5,886	$	65,422	$	675
Other liabilities	$	2	$	—	$	—	$	2

Changes in the Level 3 fair value category [Table Text Block]

The following tables present the changes in the Level 3 fair value category for the years ended December 31, 2023 and 2022.

(in millions)	Fixed Maturities		Equity Securities		Other Investments		Total
Balance at December 31, 2022	$	303	$	371	$	1	$	675
Total realized and unrealized investment gains (losses):
Reported in net realized investment gains (losses) (1)	(1)		(5)		—		(6)
Reported in other comprehensive income (loss)	6		—		—		6
Purchases, sales and settlements/maturities:
Purchases	25		4		—		29
Sales	—		—		(1)		(1)
Settlements/maturities	(26)		—		—		(26)
Gross transfers into Level 3	—		—		—		—
Gross transfers out of Level 3	(49)		(333)		—		(382)
Balance at December 31, 2023	$	258	$	37	$	—	$	295
Amount of total realized investment gains (losses) for the period included in the consolidated statement of income attributable to changes in the fair value of assets still held at the reporting date	$	—	$	—	$	—	$	—

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(1)Includes impairments on investments held at the end of the period as well as amortization on fixed maturities.

(in millions)	Fixed Maturities		Equity Securities		Other Investments		Total
Balance at December 31, 2021	$	248	$	343	$	5	$	596
Total realized and unrealized investment gains (losses):
Reported in net realized investment gains (losses) (1)	1		33		2		36
Reported in other comprehensive income (loss)	(13)		—		—		(13)
Purchases, sales and settlements/maturities:
Purchases	226		7		—		233
Sales	—		—		(1)		(1)
Settlements/maturities	(55)		—		(2)		(57)
Gross transfers into Level 3	—		3		—		3
Gross transfers out of Level 3	(104)		(15)		(3)		(122)
Balance at December 31, 2022	$	303	$	371	$	1	$	675
Amount of total realized investment gains (losses) for the period included in the consolidated statement of income attributable to changes in the fair value of assets still held at the reporting date	$	—	$	33	$	1	$	34

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(1)Includes impairments on investments held at the end of the period as well as amortization on fixed maturities.

Carrying value and fair value of the Company's financial assets and financial liabilities disclosed, but not carried, at fair value, and the level within the fair value hierarchy at which such assets and liabilities are categorized [Table Text Block]

The following tables present the carrying value and fair value of the Company’s financial assets and financial liabilities disclosed, but not carried, at fair value, and the level within the fair value hierarchy at which such assets and liabilities are categorized.

(at December 31, 2023, in millions)	Carrying Value		Fair Value		Level 1		Level 2		Level 3
Financial assets:
Short-term securities	$	5,137	$	5,137	$	1,171	$	3,912	$	54
Financial liabilities:
Debt	$	7,931	$	7,645	$	—	$	7,645	$	—
Commercial paper	100		100		—		100		—

(at December 31, 2022, in millions)	Carrying Value		Fair Value		Level 1		Level 2		Level 3
Financial assets:
Short-term securities	$	3,470	$	3,470	$	871	$	2,546	$	53
Financial liabilities:
Debt	$	7,192	$	6,509	$	—	$	6,509	$	—
Commercial paper	100		100		—		100		—