Business Segments (Income Statement Information) (Details) - USD ($) $ in Millions	12 Months Ended
	Dec. 31, 2015	Dec. 31, 2014	Dec. 31, 2013
Segment Reporting Information [Line Items]
Net written premiums	$ 6,962	$ 7,088	$ 7,348
Operating Revenues
Net earned premiums	6,921	7,212	7,271
Net investment income	1,840	2,067	2,282
Other revenues	407	356	359
Total operating revenues	9,168	9,635	9,912
Claims, Benefits and Expenses
Net incurred claims and benefits	5,372	5,577	5,793
Policyholders' dividends	12	14	13
Amortization of deferred acquisition costs	1,540	1,317	1,362
Other insurance related expenses	1,093	1,029	1,013
Other expenses	535	548	475
Total claims, benefits and expenses	8,552	8,485	8,656
Operating income (loss) from continuing operations before income tax	616	1,150	1,256
Income tax (expense) benefit on operating income (loss)	(101)	(301)	(355)
Net operating income (loss) from continuing operations	515	849	901
Net realized investment gains (losses), pre-tax	(67)	57	20
Income tax (expense) benefit on net realized investment gains (losses)	31	(18)	(6)
Net realized investment gains (losses), after tax	(36)	39	14
Net income (loss) from continuing operations	479	888	915
Specialty [Member]
Segment Reporting Information [Line Items]
Net written premiums	2,781	2,839	2,880
Operating Revenues
Net earned premiums	2,782	2,838	2,795
Net investment income	474	560	629
Other revenues	356	295	257
Total operating revenues	3,612	3,693	3,681
Claims, Benefits and Expenses
Net incurred claims and benefits	1,597	1,627	1,593
Policyholders' dividends	4	6	6
Amortization of deferred acquisition costs	589	592	585
Other insurance related expenses	278	262	250
Other expenses	301	254	237
Total claims, benefits and expenses	2,769	2,741	2,671
Operating income (loss) from continuing operations before income tax	843	952	1,010
Income tax (expense) benefit on operating income (loss)	(283)	(318)	(342)
Net operating income (loss) from continuing operations	560	634	668
Net realized investment gains (losses), pre-tax	(33)	15	(5)
Income tax (expense) benefit on net realized investment gains (losses)	11	(5)	2
Net realized investment gains (losses), after tax	(22)	10	(3)
Net income (loss) from continuing operations	538	644	665
Commercial [Member]
Segment Reporting Information [Line Items]
Net written premiums	2,818	2,817	2,960
Operating Revenues
Net earned premiums	2,788	2,906	3,004
Net investment income	593	723	899
Other revenues	37	38	96
Total operating revenues	3,418	3,667	3,999
Claims, Benefits and Expenses
Net incurred claims and benefits	1,814	2,187	2,259
Policyholders' dividends	8	8	7
Amortization of deferred acquisition costs	469	493	526
Other insurance related expenses	538	487	498
Other expenses	28	31	32
Total claims, benefits and expenses	2,857	3,206	3,322
Operating income (loss) from continuing operations before income tax	561	461	677
Income tax (expense) benefit on operating income (loss)	(192)	(154)	(229)
Net operating income (loss) from continuing operations	369	307	448
Net realized investment gains (losses), pre-tax	(47)	16	(15)
Income tax (expense) benefit on net realized investment gains (losses)	16	(6)	5
Net realized investment gains (losses), after tax	(31)	10	(10)
Net income (loss) from continuing operations	338	317	438
International [Member]
Segment Reporting Information [Line Items]
Net written premiums	822	880	959
Operating Revenues
Net earned premiums	804	913	916
Net investment income	52	61	60
Other revenues	(1)	0	0
Total operating revenues	855	974	976
Claims, Benefits and Expenses
Net incurred claims and benefits	479	488	489
Policyholders' dividends	0	0	0
Amortization of deferred acquisition costs	168	204	223
Other insurance related expenses	138	151	140
Other expenses	12	28	12
Total claims, benefits and expenses	797	871	864
Operating income (loss) from continuing operations before income tax	58	103	112
Income tax (expense) benefit on operating income (loss)	(21)	(34)	(43)
Net operating income (loss) from continuing operations	37	69	69
Net realized investment gains (losses), pre-tax	1	(1)	5
Income tax (expense) benefit on net realized investment gains (losses)	0	1	(2)
Net realized investment gains (losses), after tax	1	0	3
Net income (loss) from continuing operations	38	69	72
Life and Group Non-Core [Member]
Segment Reporting Information [Line Items]
Net written premiums	542	553	552
Operating Revenues
Net earned premiums	548	556	559
Net investment income	704	700	662
Other revenues	7	16	(4)
Total operating revenues	1,259	1,272	1,217
Claims, Benefits and Expenses
Net incurred claims and benefits	1,421	1,304	1,261
Policyholders' dividends	0	0	0
Amortization of deferred acquisition costs	314	28	28
Other insurance related expenses	142	130	130
Other expenses	11	30	13
Total claims, benefits and expenses	1,888	1,492	1,432
Operating income (loss) from continuing operations before income tax	(629)	(220)	(215)
Income tax (expense) benefit on operating income (loss)	315	151	141
Net operating income (loss) from continuing operations	(314)	(69)	(74)
Net realized investment gains (losses), pre-tax	(1)	7	26
Income tax (expense) benefit on net realized investment gains (losses)	9	0	(8)
Net realized investment gains (losses), after tax	8	7	18
Net income (loss) from continuing operations	(306)	(62)	(56)
Corporate and Other Non-Core [Member]
Segment Reporting Information [Line Items]
Net written premiums	1	1	(1)
Operating Revenues
Net earned premiums	1	1	(1)
Net investment income	17	23	32
Other revenues	11	12	12
Total operating revenues	29	36	43
Claims, Benefits and Expenses
Net incurred claims and benefits	61	(29)	191
Policyholders' dividends	0	0	0
Amortization of deferred acquisition costs	0	0	0
Other insurance related expenses	(1)	1	(3)
Other expenses	186	210	183
Total claims, benefits and expenses	246	182	371
Operating income (loss) from continuing operations before income tax	(217)	(146)	(328)
Income tax (expense) benefit on operating income (loss)	80	54	118
Net operating income (loss) from continuing operations	(137)	(92)	(210)
Net realized investment gains (losses), pre-tax	13	20	9
Income tax (expense) benefit on net realized investment gains (losses)	(5)	(8)	(3)
Net realized investment gains (losses), after tax	8	12	6
Net income (loss) from continuing operations	(129)	(80)	(204)
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	(3)	(5)	(2)
Total operating revenues	(5)	(7)	(4)
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	(3)	(5)	(2)
Total claims, benefits and expenses	(5)	(7)	(4)
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	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