Business Segments - Income Statement Information (Details) - USD ($) $ in Millions	3 Months Ended
	Mar. 31, 2017	Mar. 31, 2016
Operating revenues
Net earned premiums	$ 1,645	$ 1,699
Net investment income	545	435
Other revenues	104	97
Total operating revenues	2,294	2,231
Claims, Benefits and Expenses
Net incurred claims and benefits	1,289	1,404
Policyholders’ dividends	4	4
Amortization of deferred acquisition costs	305	307
Other insurance related expenses	254	277
Other expenses	135	146
Total claims, benefits and expenses	1,987	2,138
Operating income (loss) before income tax	307	93
Income tax (expense) benefit on operating income (loss)	(72)	(2)
Net operating income (loss)	235	91
Net realized investment gains (losses)	36	(36)
Income tax (expense) benefit on net realized investment gains (losses)	(11)	11
Net realized investment gains (losses), after tax	25	(25)
Net income (loss)	260	66
Operating Segments | Specialty
Operating revenues
Net earned premiums	664	682
Net investment income	153	107
Other revenues	94	87
Total operating revenues	911	876
Claims, Benefits and Expenses
Net incurred claims and benefits	386	390
Policyholders’ dividends	1	1
Amortization of deferred acquisition costs	143	144
Other insurance related expenses	69	75
Other expenses	81	75
Total claims, benefits and expenses	680	685
Operating income (loss) before income tax	231	191
Income tax (expense) benefit on operating income (loss)	(77)	(64)
Net operating income (loss)	154	127
Net realized investment gains (losses)	7	(11)
Income tax (expense) benefit on net realized investment gains (losses)	(3)	4
Net realized investment gains (losses), after tax	4	(7)
Net income (loss)	158	120
Operating Segments | Commercial
Operating revenues
Net earned premiums	651	688
Net investment income	178	126
Other revenues	9	6
Total operating revenues	838	820
Claims, Benefits and Expenses
Net incurred claims and benefits	437	442
Policyholders’ dividends	3	3
Amortization of deferred acquisition costs	116	116
Other insurance related expenses	126	141
Other expenses	14	5
Total claims, benefits and expenses	696	707
Operating income (loss) before income tax	142	113
Income tax (expense) benefit on operating income (loss)	(48)	(39)
Net operating income (loss)	94	74
Net realized investment gains (losses)	11	(18)
Income tax (expense) benefit on net realized investment gains (losses)	(3)	6
Net realized investment gains (losses), after tax	8	(12)
Net income (loss)	102	62
Operating Segments | International
Operating revenues
Net earned premiums	197	198
Net investment income	12	12
Other revenues	0	1
Total operating revenues	209	211
Claims, Benefits and Expenses
Net incurred claims and benefits	115	121
Policyholders’ dividends	0	0
Amortization of deferred acquisition costs	46	47
Other insurance related expenses	27	28
Other expenses	(6)	9
Total claims, benefits and expenses	182	205
Operating income (loss) before income tax	27	6
Income tax (expense) benefit on operating income (loss)	(7)	0
Net operating income (loss)	20	6
Net realized investment gains (losses)	6	4
Income tax (expense) benefit on net realized investment gains (losses)	(1)	(1)
Net realized investment gains (losses), after tax	5	3
Net income (loss)	25	9
Operating Segments | Life & Group Non-Core
Operating revenues
Net earned premiums	133	131
Net investment income	197	187
Other revenues	1	0
Total operating revenues	331	318
Claims, Benefits and Expenses
Net incurred claims and benefits	330	323
Policyholders’ dividends	0	0
Amortization of deferred acquisition costs	0	0
Other insurance related expenses	32	33
Other expenses	2	3
Total claims, benefits and expenses	364	359
Operating income (loss) before income tax	(33)	(41)
Income tax (expense) benefit on operating income (loss)	37	39
Net operating income (loss)	4	(2)
Net realized investment gains (losses)	10	(3)
Income tax (expense) benefit on net realized investment gains (losses)	(4)	0
Net realized investment gains (losses), after tax	6	(3)
Net income (loss)	10	(5)
Operating Segments | Corporate & Other Non-Core
Operating revenues
Net earned premiums	0	0
Net investment income	5	3
Other revenues	0	3
Total operating revenues	5	6
Claims, Benefits and Expenses
Net incurred claims and benefits	21	128
Policyholders’ dividends	0	0
Amortization of deferred acquisition costs	0	0
Other insurance related expenses	0	0
Other expenses	44	54
Total claims, benefits and expenses	65	182
Operating income (loss) before income tax	(60)	(176)
Income tax (expense) benefit on operating income (loss)	23	62
Net operating income (loss)	(37)	(114)
Net realized investment gains (losses)	2	(8)
Income tax (expense) benefit on net realized investment gains (losses)	0	2
Net realized investment gains (losses), after tax	2	(6)
Net income (loss)	(35)	(120)
Intersegment Eliminations
Operating revenues
Net earned premiums	0	0
Net investment income	0	0
Other revenues	0	0
Total operating revenues	0	0
Claims, Benefits and Expenses
Net incurred claims and benefits	0	0
Policyholders’ dividends	0	0
Amortization of deferred acquisition costs	0	0
Other insurance related expenses	0	0
Other expenses	0	0
Total claims, benefits and expenses	0	0
Operating income (loss) before income tax	0	0
Income tax (expense) benefit on operating income (loss)	0	0
Net operating income (loss)	0	0
Net realized investment gains (losses)	0	0
Income tax (expense) benefit on net realized investment gains (losses)	0	0
Net realized investment gains (losses), after tax	0	0
Net income (loss)	$ 0	$ 0