Invested Assets (Tables)

12 Months Ended

Dec. 31, 2011

Invested Assets and Related Income [Abstract]

Amortized cost and fair value of fixed maturities and equity securities

	December 31, 2011
			Gross		Gross
	Amortized		Unrealized		Unrealized		Fair
	Cost		Appreciation		Depreciation		Value
	(in millions)
Fixed maturities
Tax exempt	$	18,786	$	1,462	$	37	$	20,211
Taxable
U.S. government and government agency and authority obligations		813		57		2		868
Corporate bonds		6,049		440		24		6,465
Foreign government and government agency obligations		6,409		416		2		6,823
Residential mortgage-backed securities		821		41		7		855
Commercial mortgage-backed securities		1,884		79		1		1,962
		15,976		1,033		36		16,973
Total fixed maturities	$	34,762	$	2,495	$	73	$	37,184
Equity securities	$	1,264	$	319	$	71	$	1,512

	December 31, 2010
			Gross		Gross
	Amortized		Unrealized		Unrealized		Fair
	Cost		Appreciation		Depreciation		Value
	(in millions)
Fixed maturities
Tax exempt	$	19,072	$	824	$	122	$	19,774
Taxable
U.S. government and government agency and authority obligations		807		31		9		829
Corporate bonds		6,025		405		20		6,410
Foreign government and government agency obligations		6,176		237		14		6,399
Residential mortgage-backed securities		1,293		63		6		1,350
Commercial mortgage-backed securities		1,688		70		1		1,757
		15,989		806		50		16,745
Total fixed maturities	$	35,061	$	1,630	$	172	$	36,519
Equity securities	$	1,285	$	340	$	75	$	1,550

Fair value and amortized cost for the tax exempt fixed maturities other than pre-refunded bonds for each state in which the Corporation's aggregate investment was 5% or more of total tax exempt fixed maturities

	Fair Value
			Municipal
			and Political
	Special		Subdivision		State
	Revenue		General		General				Amortized
State	Bonds		Obligations		Obligations		Total		Cost
	(in millions)
Texas	$	1,035	$	1,156	$	275	$	2,466	$	2,269
New York		1,385		139		36		1,560		1,444
California		994		140		240		1,374		1,278
Illinois		617		486		74		1,177		1,102

Fair value and amortized cost for the foreign government and government agency fixed maturities for each country in which the Corporation's aggregate investment was 5% or more of total foreign government and government agency fixed maturities

	Fair		Amortized
Country	Value		Cost
	(in millions)
Canada	$	2,075	$	1,943
United Kingdom		1,275		1,145
Germany		897		855
Australia		623		579

Fair value and amortized cost of fixed maturities by contractual maturity

			Amortized
	Fair Value		Cost
	(in millions)
Due in one year or less	$	2,439	$	2,401
Due after one year through five years		11,916		11,279
Due after five years through ten years		12,356		11,215
Due after ten years		7,656		7,162
		34,367		32,057
Residential mortgage-backed securities		855		821
Commercial mortgage-backed securities		1,962		1,884
	$	37,184	$	34,762

Components of unrealized appreciation or depreciation of investments

	December 31
	2011		2010
	(in millions)
Fixed maturities
Gross unrealized appreciation	$	2,495	$	1,630
Gross unrealized depreciation		73		172
		2,422		1,458
Equity securities
Gross unrealized appreciation		319		340
Gross unrealized depreciation		71		75
		248		265
		2,670		1,723
Deferred income tax liability		934		603
	$	1,736	$	1,120

Fair value and gross unrealized depreciation of investments in an unrealized loss position

The following table summarizes, for all investment securities in an unrealized loss position at December 31, 2011, the aggregate fair value and gross unrealized depreciation, including unrealized other-than-temporary impairment losses, by investment category and length of time that individual securities have continuously been in an unrealized loss position.

	Less Than 12 Months				12 Months or More				Total
			Gross				Gross				Gross
	Fair		Unrealized		Fair		Unrealized		Fair		Unrealized
	Value		Depreciation		Value		Depreciation		Value		Depreciation
					(in millions)
Fixed maturities
Tax exempt	$	81	$	1	$	240	$	36	$	321	$	37
Taxable
U.S. government and government agency and authority obligations		19		1		18		1		37		2
Corporate bonds		489		14		176		10		665		24
Foreign government and government agency obligations		499		1		21		1		520		2
Residential mortgage-backed securities		77		2		22		5		99		7
Commercial mortgage-backed securities		34		1		—		—		34		1
		1,118		19		237		17		1,355		36
Total fixed maturities		1,199		20		477		53		1,676		73
Equity securities		231		45		199		26		430		71
	$	1,430	$	65	$	676	$	79	$	2,106	$	144

	Less Than 12 Months				12 Months or More				Total
			Gross				Gross				Gross
	Fair		Unrealized		Fair		Unrealized		Fair		Unrealized
	Value		Depreciation		Value		Depreciation		Value		Depreciation
					(in millions)
Fixed maturities
Tax exempt	$	2,498	$	79	$	284	$	43	$	2,782	$	122
Taxable
U.S. government and government agency and authority obligations		111		3		45		6		156		9
Corporate bonds		448		11		166		9		614		20
Foreign government and government agency obligations		1,016		13		27		1		1,043		14
Residential mortgage-backed securities		9		1		41		5		50		6
Commercial mortgage-backed securities		38		1		—		—		38		1
		1,622		29		279		21		1,901		50
Total fixed maturities		4,120		108		563		64		4,683		172
Equity securities		69		14		299		61		368		75
	$	4,189	$	122	$	862	$	125	$	5,051	$	247

Change in unrealized appreciation or depreciation of investments carried at fair value

	Years Ended December 31
	2011			2010		2009
	(in millions)
Change in unrealized appreciation of fixed maturities	$	964		$	70	$	1,524
Change in unrealized appreciation of equity securities		(17	)		47		302
		947			117		1,826
Deferred income tax		331			41		639
	$	616		$	76	$	1,187

Sources of net investment income

	Years Ended December 31
	2011		2010		2009
	(in millions)
Fixed maturities	$	1,549	$	1,564	$	1,548
Equity securities		34		47		35
Short term investments		16		9		21
Other		45		45		45
Gross investment income		1,644		1,665		1,649
Investment expenses		39		35		39
	$	1,605	$	1,630	$	1,610

Realized investment gains and losses

	Years Ended December 31
	2011			2010			2009
	(in millions)
Fixed maturities
Gross realized gains	$	70		$	98		$	110
Gross realized losses		(39	)		(26	)		(38	)
Other-than-temporary impairment losses		(1	)		(5	)		(23	)
		30			67			49
Equity securities
Gross realized gains		74			50			84
Gross realized losses		(1	)		(1	)		—
Other-than-temporary impairment losses		(22	)		(6	)		(89	)
		51			43			(5	)
Other invested assets		207			316			(21	)
	$	288		$	426		$	23