Investments (tables)

12 Months Ended

Dec. 31, 2016

Investments disclosure

Amortized cost and fair value of investments in fixed maturities [Table Text Block]

Amortized

Gross Unrealized

Fair

(at December 31, 2016, in millions)

Cost

Gains

Losses

Value

U.S. Treasury securities and obligations of U.S. government and government agencies and authorities

2,031

2,035

Obligations of states, municipalities and political subdivisions:

Local general obligation

13,955

271

182

14,044

Revenue

10,910

215

147

10,978

State general obligation

1,717

1,731

Pre-refunded

4,968

190

5,157

Total obligations of states, municipalities and political subdivisions

31,550

712

352

31,910

Debt securities issued by foreign governments

1,631

1,662

Mortgage-backed securities, collateralized mortgage obligations and pass-through securities

1,614

100

1,708

All other corporate bonds

22,737

508

138

23,107

Redeemable preferred stock

—

Total

59,650

1,369

504

60,515

	Amortized		Gross Unrealized				Fair
(at December 31, 2015, in millions)	Cost		Gains		Losses		Value
U.S. Treasury securities and obligations of U.S. government and government agencies and authorities	$	2,202	$	8	$	16	$	2,194
Obligations of states, municipalities and political subdivisions:
Local general obligation	12,744		577		3		13,318
Revenue	9,492		472		4		9,960
State general obligation	1,978		97		2		2,073
Pre-refunded	5,813		247		—		6,060
Total obligations of states, municipalities and political subdivisions	30,027		1,393		9		31,411

Debt securities issued by foreign governments	1,829		45		1		1,873
Mortgage-backed securities, collateralized mortgage obligations and pass-through securities	1,863		124		6		1,981
All other corporate bonds	22,854		523		288		23,089
Redeemable preferred stock	103		7		—		110
Total	$	58,878	$	2,100	$	320	$	60,658

Amortized cost and fair value of fixed maturities by contractual maturity [Table Text Block]

(at December 31, 2016, in millions)	Amortized Cost		Fair Value
Due in one year or less	$	5,619	$	5,677
Due after 1 year through 5 years	16,417		16,926
Due after 5 years through 10 years	14,258		14,449
Due after 10 years	21,742		21,755
	58,036		58,807
Mortgage-backed securities, collateralized mortgage obligations and pass-through securities	1,614		1,708
Total	$	59,650	$	60,515

Cost and fair value of investments in equity securities [Table Text Block]

			Gross Unrealized				Fair
(at December 31, 2016, in millions)	Cost		Gains		Losses		Value
Public common stock	$	390	$	216	$	3	$	603
Non-redeemable preferred stock	114		20		5		129
Total	$	504	$	236	$	8	$	732

			Gross Unrealized				Fair
(at December 31, 2015, in millions)	Cost		Gains		Losses		Value
Public common stock	$	386	$	164	$	7	$	543
Non-redeemable preferred stock	142		26		6		162
Total	$	528	$	190	$	13	$	705

Unrealized investment losses [Table Text Block]

	Less than 12 months				12 months or longer				Total
(at December 31, 2016, in millions)	Fair Value		Gross Unrealized Losses		Fair Value		Gross Unrealized Losses		Fair Value		Gross Unrealized Losses
Fixed maturities
U.S. Treasury securities and obligations of U.S. government and government agencies and authorities	$	1,124	$	5	$	—	$	—	$	1,124	$	5
Obligations of states, municipalities and political subdivisions	9,781		352		12		—		9,793		352
Debt securities issued by foreign governments	360		3		—		—		360		3
Mortgage-backed securities, collateralized mortgage obligations and pass-through securities	528		5		43		1		571		6
All other corporate bonds	6,470		115		437		23		6,907		138
Redeemable preferred stock	—		—		—		—		—		—
Total fixed maturities	18,263		480		492		24		18,755		504

Equity securities
Public common stock	45		2		10		1		55		3
Non-redeemable preferred stock	2		—		59		5		61		5
Total equity securities	47		2		69		6		116		8
Total	$	18,310	$	482	$	561	$	30	$	18,871	$	512

	Less than 12 months				12 months or longer				Total
(at December 31, 2015, in millions)	Fair Value		Gross Unrealized Losses		Fair Value		Gross Unrealized Losses		Fair Value		Gross Unrealized Losses
Fixed maturities
U.S. Treasury securities and obligations of U.S. government and government agencies and authorities	$	1,820	$	15	$	28	$	1	$	1,848	$	16
Obligations of states, municipalities and political subdivisions	928		7		142		2		1,070		9
Debt securities issued by foreign governments	172		1		—		—		172		1
Mortgage-backed securities, collateralized mortgage obligations and pass-through securities	473		4		57		2		530		6
All other corporate bonds	7,725		197		710		91		8,435		288
Redeemable preferred stock	8		—		—		—		8		—
Total fixed maturities	11,126		224		937		96		12,063		320

Equity securities
Public common stock	48		6		33		1		81		7
Non-redeemable preferred stock	47		3		38		3		85		6
Total equity securities	95		9		71		4		166		13
Total	$	11,221	$	233	$	1,008	$	100	$	12,229	$	333

Securities continuously in an unrealized loss position of greater than 20% of amortized cost by length of time [Table Text Block]

	Period For Which Fair Value Is Less Than 80% of Amortized Cost
(in millions)	3 Months or Less		Greater Than 3 Months, 6 Months or Less		Greater Than 6 Months, 12 Months or Less		Greater Than 12 Months		Total
Fixed maturities
Mortgage-backed securities	$	—	$	—	$	—	$	—	$	—
Other	1		—		—		2		3
Total fixed maturities	1		—		—		2		3
Equity securities	1		—		—		—		1
Total	$	2	$	—	$	—	$	2	$	4

Impairment charges included in net realized investment gains [Table Text Block]

(for the year ended December 31, in millions)	2016		2015		2014
Fixed maturities
U.S. Treasury securities and obligations of U.S. government and government agencies and authorities	$	—	$	—	$	—
Obligations of states, municipalities and political subdivisions	—		—		—
Debt securities issued by foreign governments	—		—		—
Mortgage-backed securities, collateralized mortgage obligations and pass-through securities	—		—		1
All other corporate bonds	15		13		15
Redeemable preferred stock	—		—		—
Total fixed maturities	15		13		16

Equity securities
Public common stock	9		37		9
Non-redeemable preferred stock	3		—		—
Total equity securities	12		37		9

Other investments	2		2		1
Total	$	29	$	52	$	26

Cumulative amount of and the changes during the year in the credit losses of other-than-temporary impairments (OTTI) on fixed maturities recognized in the consolidated statement of income for which a portion of the OTTI was recognized in other comprehensive income (loss) [Table Text Block]

Year ended December 31, 2016 (in millions)	Cumulative OTTI Credit Losses Recognized for Securities Held, Beginning of Period		Additions for OTTI Securities Where No Credit Losses Were Previously Recognized		Additions for OTTI Securities Where Credit Losses Have Been Previously Recognized		Reductions Due to Sales/Defaults of Credit- Impaired Securities			Adjustments to Book Value of Credit- Impaired Securities due to Changes in Cash Flows			Cumulative OTTI Credit Losses Recognized for Securities Still Held, End of Period
Fixed maturities
Mortgage-backed securities, collateralized mortgage obligations and pass-through securities	$	32	$	—	$	—	$	—		$	(1	)	$	31
All other corporate bonds	51		13		—		(7		)	(3		)	54
Total fixed maturities	$	83	$	13	$	—	$	(7	)	$	(4	)	$	85

Year ended December 31, 2015 (in millions)	Cumulative OTTI Credit Losses Recognized for Securities Held, Beginning of Period		Additions for OTTI Securities Where No Credit Losses Were Previously Recognized		Additions for OTTI Securities Where Credit Losses Have Been Previously Recognized		Reductions Due to Sales/Defaults of Credit- Impaired Securities			Adjustments to Book Value of Credit- Impaired Securities due to Changes in Cash Flows			Cumulative OTTI Credit Losses Recognized for Securities Still Held, End of Period
Fixed maturities
Mortgage-backed securities, collateralized mortgage obligations and pass-through securities	$	40	$	—	$	—	$	(6	)	$	(2	)	$	32
All other corporate bonds	59		2		—		(4		)	(6		)	51
Total fixed maturities	$	99	$	2	$	—	$	(10	)	$	(8	)	$	83

Net investment income [Table Text Block]

(for the year ended December 31, in millions)	2016		2015		2014
Gross investment income
Fixed maturities	$	1,981	$	2,091	$	2,244
Equity securities	37		39		40
Short-term securities	29		12		9
Real estate investments	51		48		44
Other investments	242		230		489
Gross investment income	2,340		2,420		2,826
Investment expenses	38		41		39
Net investment income	$	2,302	$	2,379	$	2,787

Changes in net unrealized investment gains [Table Text Block]

(at and for the year ended December 31, in millions)	2016			2015			2014
Changes in net unrealized investment gains
Fixed maturities	$	(915	)	$	(893	)	$	913
Equity securities	51			(143		)	63
Other investments	2			2			2
Change in net pre-tax unrealized gains on investment securities	(862		)	(1,034		)	978
Related tax expense (benefit)	(303		)	(357		)	334
Change in net unrealized gains on investment securities	(559		)	(677		)	644
Balance, beginning of year	1,289			1,966			1,322
Balance, end of year	$	730		$	1,289		$	1,966