Business Segments (Income Statement Information) (Details) (USD $) In Millions, unless otherwise specified	12 Months Ended
	Dec. 31, 2014	Dec. 31, 2013	Dec. 31, 2012
Segment Reporting Information [Line Items]
Net written premiums	$ 7,088	$ 7,348	$ 6,964
Operating Revenues
Net earned premiums	7,212	7,271	6,881
Net investment income	2,067	2,282	2,110
Other revenues	356	359	319
Total operating revenues	9,635	9,912	9,310
Claims, Benefits and Expenses
Net incurred claims and benefits	5,577	5,793	5,716
Policyholders' dividends	14	13	13
Amortization of deferred acquisition costs	1,317	1,362	1,274
Other insurance related expenses	1,029	1,013	1,047
Other expenses	548	475	455
Total claims, benefits and expenses	8,485	8,656	8,505
Operating income (loss) from continuing operations before income tax	1,150	1,256	805
Income tax (expense) benefit on operating income (loss)	(301)	(355)	(220)
Net operating income (loss) from continuing operations	849	901	585
Net realized investment gains (losses), pre-tax	57	20	54
Income tax (expense) benefit on net realized investment gains (losses)	(18)	(6)	(19)
Net realized investment gains (losses), after tax	39	14	35
Net income (loss) from continuing operations	888	915	620
Specialty [Member]
Segment Reporting Information [Line Items]
Net written premiums	2,839	2,880	2,733
Operating Revenues
Net earned premiums	2,838	2,795	2,709
Net investment income	560	629	564
Other revenues	295	257	231
Total operating revenues	3,693	3,681	3,504
Claims, Benefits and Expenses
Net incurred claims and benefits	1,627	1,593	1,746
Policyholders' dividends	6	6	2
Amortization of deferred acquisition costs	592	585	574
Other insurance related expenses	262	250	278
Other expenses	254	237	207
Total claims, benefits and expenses	2,741	2,671	2,807
Operating income (loss) from continuing operations before income tax	952	1,010	697
Income tax (expense) benefit on operating income (loss)	(318)	(342)	(235)
Net operating income (loss) from continuing operations	634	668	462
Net realized investment gains (losses), pre-tax	15	(5)	18
Income tax (expense) benefit on net realized investment gains (losses)	(5)	2	(8)
Net realized investment gains (losses), after tax	10	(3)	10
Net income (loss) from continuing operations	644	665	472
Commercial [Member]
Segment Reporting Information [Line Items]
Net written premiums	2,817	2,960	3,033
Operating Revenues
Net earned premiums	2,906	3,004	2,968
Net investment income	723	899	826
Other revenues	38	96	41
Total operating revenues	3,667	3,999	3,835
Claims, Benefits and Expenses
Net incurred claims and benefits	2,187	2,259	2,370
Policyholders' dividends	8	7	11
Amortization of deferred acquisition costs	493	526	520
Other insurance related expenses	487	498	532
Other expenses	31	32	37
Total claims, benefits and expenses	3,206	3,322	3,470
Operating income (loss) from continuing operations before income tax	461	677	365
Income tax (expense) benefit on operating income (loss)	(154)	(229)	(120)
Net operating income (loss) from continuing operations	307	448	245
Net realized investment gains (losses), pre-tax	16	(15)	34
Income tax (expense) benefit on net realized investment gains (losses)	(6)	5	(11)
Net realized investment gains (losses), after tax	10	(10)	23
Net income (loss) from continuing operations	317	438	268
International [Member]
Segment Reporting Information [Line Items]
Net written premiums	880	959	648	[1]
Operating Revenues
Net earned premiums	913	916	647	[1]
Net investment income	61	60	59	[1]
Other revenues	0	0	(1)	[1]
Total operating revenues	974	976	705	[1]
Claims, Benefits and Expenses
Net incurred claims and benefits	488	489	361	[1]
Policyholders' dividends	0	0	0	[1]
Amortization of deferred acquisition costs	204	223	152	[1]
Other insurance related expenses	151	140	94	[1]
Other expenses	28	12	7	[1]
Total claims, benefits and expenses	871	864	614	[1]
Operating income (loss) from continuing operations before income tax	103	112	91	[1]
Income tax (expense) benefit on operating income (loss)	(34)	(43)	(40)	[1]
Net operating income (loss) from continuing operations	69	69	51	[1]
Net realized investment gains (losses), pre-tax	(1)	5	7	[1]
Income tax (expense) benefit on net realized investment gains (losses)	1	(2)	(1)	[1]
Net realized investment gains (losses), after tax	0	3	6	[1]
Net income (loss) from continuing operations	69	72	57	[1]
Life and Group Non-Core [Member]
Segment Reporting Information [Line Items]
Net written premiums	553	552	553
Operating Revenues
Net earned premiums	556	559	559
Net investment income	700	662	629
Other revenues	16	(4)	33
Total operating revenues	1,272	1,217	1,221
Claims, Benefits and Expenses
Net incurred claims and benefits	1,304	1,261	1,255
Policyholders' dividends	0	0	0
Amortization of deferred acquisition costs	28	28	28
Other insurance related expenses	130	130	142
Other expenses	30	13	22
Total claims, benefits and expenses	1,492	1,432	1,447
Operating income (loss) from continuing operations before income tax	(220)	(215)	(226)
Income tax (expense) benefit on operating income (loss)	151	141	134
Net operating income (loss) from continuing operations	(69)	(74)	(92)
Net realized investment gains (losses), pre-tax	7	26	(9)
Income tax (expense) benefit on net realized investment gains (losses)	0	(8)	3
Net realized investment gains (losses), after tax	7	18	(6)
Net income (loss) from continuing operations	(62)	(56)	(98)
Corporate and Other Non-Core [Member]
Segment Reporting Information [Line Items]
Net written premiums	1	(1)	(1)
Operating Revenues
Net earned premiums	1	(1)	0
Net investment income	23	32	32
Other revenues	12	12	16
Total operating revenues	36	43	48
Claims, Benefits and Expenses
Net incurred claims and benefits	(29)	191	(16)
Policyholders' dividends	0	0	0
Amortization of deferred acquisition costs	0	0	0
Other insurance related expenses	1	(3)	3
Other expenses	210	183	183
Total claims, benefits and expenses	182	371	170
Operating income (loss) from continuing operations before income tax	(146)	(328)	(122)
Income tax (expense) benefit on operating income (loss)	54	118	41
Net operating income (loss) from continuing operations	(92)	(210)	(81)
Net realized investment gains (losses), pre-tax	20	9	4
Income tax (expense) benefit on net realized investment gains (losses)	(8)	(3)	(2)
Net realized investment gains (losses), after tax	12	6	2
Net income (loss) from continuing operations	(80)	(204)	(79)
Eliminations [Member]
Segment Reporting Information [Line Items]
Net written premiums	(2)	(2)	(2)
Operating Revenues
Net earned premiums	(2)	(2)	(2)
Net investment income	0	0	0
Other revenues	(5)	(2)	(1)
Total operating revenues	(7)	(4)	(3)
Claims, Benefits and Expenses
Net incurred claims and benefits	0	0	0
Policyholders' dividends	0	0	0
Amortization of deferred acquisition costs	0	0	0
Other insurance related expenses	(2)	(2)	(2)
Other expenses	(5)	(2)	(1)
Total claims, benefits and expenses	(7)	(4)	(3)
Operating income (loss) from continuing operations before income tax	0	0	0
Income tax (expense) benefit on operating income (loss)	0	0	0
Net operating income (loss) from continuing operations		0	0
Net realized investment gains (losses), pre-tax	0	0	0
Income tax (expense) benefit on net realized investment gains (losses)	0	0	0
Net realized investment gains (losses), after tax	0	0	0
Net income (loss) from continuing operations	$ 0	$ 0	$ 0

[1] International includes Hardy from the date of acquisition.