Fair Value Measurements (Tables)

3 Months Ended

Mar. 31, 2018

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.  An investment transferred between levels during a period is transferred at its fair value as of the beginning of that period.

(at March 31, 2018, 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	$	2,034	$	2,034	$	—	$	—
Obligations of states, municipalities and political subdivisions	29,440		—		29,428		12
Debt securities issued by foreign governments	1,327		—		1,327		—
Mortgage-backed securities, collateralized mortgage obligations and pass-through securities	2,531		—		2,491		40
All other corporate bonds	26,842		1		26,646		195
Redeemable preferred stock	92		3		89		—
Total fixed maturities	62,266		2,038		59,981		247
Equity securities
Public common stock	324		324		—		—
Non-redeemable preferred stock	106		42		64		—
Total equity securities	430		366		64		—
Other investments	55		17		—		38
Total	$	62,751	$	2,421	$	60,045	$	285

(at December 31, 2017, 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	$	2,076	$	2,076	$	—	$	—
Obligations of states, municipalities and political subdivisions	30,915		—		30,910		5
Debt securities issued by foreign governments	1,509		—		1,509		—
Mortgage-backed securities, collateralized mortgage obligations and pass-through securities	2,410		—		2,371		39
All other corporate bonds	25,689		11		25,518		160
Redeemable preferred stock	95		3		92		—
Total fixed maturities	62,694		2,090		60,400		204
Equity securities
Public common stock	339		339		—		—
Non-redeemable preferred stock	114		45		69		—
Total equity securities	453		384		69		—
Other investments	57		19		—		38
Total	$	63,204	$	2,493	$	60,469	$	242

Carrying value and fair value of financial instruments disclosed, but not carried, at fair value and the level within the fair value hierarchy at which such financial instruments 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 March 31, 2018, in millions)	Carrying Value		Fair Value		Level 1		Level 2		Level 3
Financial assets:
Short-term securities	$	4,486	$	4,486	$	835	$	3,612	$	39
Financial liabilities:
Debt	$	6,963	$	7,835	$	—	$	7,835	$	—

(at December 31, 2017, in millions)	Carrying Value		Fair Value		Level 1		Level 2		Level 3
Financial assets:
Short-term securities	$	4,895	$	4,895	$	1,238	$	3,622	$	35
Financial liabilities:
Debt	$	6,471	$	7,702	$	—	$	7,702	$	—
Commercial paper	$	100	$	100	$	—	$	100	$	—