Fair Value Measurements (Tables)

12 Months Ended

Dec. 31, 2020

Fair Value Disclosures [Abstract]

Level within the fair value hierarchy at which the Company's financial assets and financial liabilities reported at fair value 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, 2020, 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	$	2,149	$	2,149	$	—	$	—
Obligations of states, municipalities and political subdivisions	36,360		—		36,349		11
Debt securities issued by foreign governments	1,054		—		1,054		—
Mortgage-backed securities, collateralized mortgage obligations and pass-through securities	2,361		—		2,361		—
All other corporate bonds	32,054		—		31,899		155
Redeemable preferred stock	25		3		22		—
Total fixed maturities	74,003		2,152		71,685		166
Equity securities
Public common stock	410		410		—		—
Non-redeemable preferred stock	43		18		25		—
Total equity securities	453		428		25		—
Other investments	52		17		—		35
Total	$	74,508	$	2,597	$	71,710	$	201
Other liabilities	$	5	$	—	$	—	$	5

(at December 31, 2019, 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	$	2,095	$	2,095	$	—	$	—
Obligations of states, municipalities and political subdivisions	29,917		—		29,905		12
Debt securities issued by foreign governments	1,173		—		1,173		—
Mortgage-backed securities, collateralized mortgage obligations and pass-through securities	3,280		—		3,280		—
All other corporate bonds	31,619		—		31,530		89
Redeemable preferred stock	50		—		50		—
Total fixed maturities	68,134		2,095		65,938		101
Equity securities
Public common stock	383		383		—		—
Non-redeemable preferred stock	42		13		29		—
Total equity securities	425		396		29		—
Other investments	36		16		—		20
Total	$	68,595	$	2,507	$	65,967	$	121
Other liabilities	$	8	$	—	$	—	$	8

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, 2020 and 2019.

(in millions)	Fixed Maturities		Other Investments		Total
Balance at December 31, 2019	$	101	$	20	$	121
Total realized and unrealized investment gains (losses):
Reported in net realized investment gains (1)	(1)		—		(1)
Reported in increases in other comprehensive income (loss)	2		—		2
Purchases, sales and settlements/maturities:
Purchases	79		16		95
Sales	—		(1)		(1)
Settlements/maturities	(15)		—		(15)
Gross transfers into Level 3	3		—		3
Gross transfers out of Level 3	(3)		—		(3)
Balance at December 31, 2020	$	166	$	35	$	201
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		Other Investments		Total
Balance at December 31, 2018	$	186	$	36	$	222
Total realized and unrealized investment gains (losses):
Reported in net realized investment gains (1)	—		3		3
Reported in increases in other comprehensive income (loss)	4		—		4
Purchases, sales and settlements/maturities:
Purchases	38		6		44
Sales	(1)		(25)		(26)
Settlements/maturities	(19)		—		(19)
Gross transfers into Level 3	—		—		—
Gross transfers out of Level 3	(107)		—		(107)
Balance at December 31, 2019	$	101	$	20	$	121
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.

Carrying value and fair value of 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, 2020, in millions)	Carrying Value		Fair Value		Level 1		Level 2		Level 3
Financial assets:
Short-term securities	$	5,511	$	5,511	$	630	$	4,829	$	52
Financial liabilities:
Debt	$	6,450	$	8,976	$	—	$	8,976	$	—
Commercial paper	100		100		—		100		—

(at December 31, 2019, in millions)	Carrying Value		Fair Value		Level 1		Level 2		Level 3
Financial assets:
Short-term securities	$	4,943	$	4,943	$	685	$	4,204	$	54
Financial liabilities:
Debt	$	6,458	$	8,049	$	—	$	8,049	$	—
Commercial paper	100		100		—		100		—