Business Segments (Income Statement Information) (Details) - USD ($) $ in Millions	12 Months Ended
	Dec. 31, 2016	Dec. 31, 2015	Dec. 31, 2014
Segment Reporting Information [Line Items]
Net written premiums	$ 6,988	$ 6,962	$ 7,088
Operating Revenues
Net earned premiums	6,924	6,921	7,212
Net Investment Income	1,988	1,840	2,067
Other revenues	404	407	356
Total operating revenues	9,316	9,168	9,635
Claims, Benefits and Expenses
Net incurred claims and benefits	5,270	5,372	5,577
Policyholders' dividends	13	12	14
Amortization of deferred acquisition costs	1,235	1,540	1,317
Other insurance related expenses	1,122	1,093	1,029
Other expenses	589	535	548
Total claims, benefits and expenses	8,229	8,552	8,485
Operating income (loss) from continuing operations before income tax	1,087	616	1,150
Income tax (expense) benefit on operating income (loss)	(263)	(101)	(301)
Net operating income (loss) from continuing operations	824	515	849
Net realized investment gains (losses), pre-tax	50	(67)	57
Income tax (expense) benefit on net realized investment gains (losses)	(15)	31	(18)
Net realized investment gains (losses), after tax	35	(36)	39
Net income (loss) from continuing operations	859	479	888
Specialty [Member]
Segment Reporting Information [Line Items]
Net written premiums	2,780	2,781	2,839
Operating Revenues
Net earned premiums	2,779	2,782	2,838
Net Investment Income	516	474	560
Other revenues	362	356	295
Total operating revenues	3,657	3,612	3,693
Claims, Benefits and Expenses
Net incurred claims and benefits	1,467	1,597	1,627
Policyholders' dividends	4	4	6
Amortization of deferred acquisition costs	591	589	592
Other insurance related expenses	301	278	262
Other expenses	312	301	254
Total claims, benefits and expenses	2,675	2,769	2,741
Operating income (loss) from continuing operations before income tax	982	843	952
Income tax (expense) benefit on operating income (loss)	(332)	(283)	(318)
Net operating income (loss) from continuing operations	650	560	634
Net realized investment gains (losses), pre-tax	5	(33)	15
Income tax (expense) benefit on net realized investment gains (losses)	(2)	11	(5)
Net realized investment gains (losses), after tax	3	(22)	10
Net income (loss) from continuing operations	653	538	644
Commercial [Member]
Segment Reporting Information [Line Items]
Net written premiums	2,841	2,818	2,817
Operating Revenues
Net earned premiums	2,804	2,788	2,906
Net Investment Income	638	593	723
Other revenues	32	37	38
Total operating revenues	3,474	3,418	3,667
Claims, Benefits and Expenses
Net incurred claims and benefits	1,927	1,814	2,187
Policyholders' dividends	9	8	8
Amortization of deferred acquisition costs	470	469	493
Other insurance related expenses	560	538	487
Other expenses	36	28	31
Total claims, benefits and expenses	3,002	2,857	3,206
Operating income (loss) from continuing operations before income tax	472	561	461
Income tax (expense) benefit on operating income (loss)	(161)	(192)	(154)
Net operating income (loss) from continuing operations	311	369	307
Net realized investment gains (losses), pre-tax	4	(47)	16
Income tax (expense) benefit on net realized investment gains (losses)	(2)	16	(6)
Net realized investment gains (losses), after tax	2	(31)	10
Net income (loss) from continuing operations	313	338	317
International [Member]
Segment Reporting Information [Line Items]
Net written premiums	821	822	880
Operating Revenues
Net earned premiums	806	804	913
Net Investment Income	51	52	61
Other revenues	0	(1)	0
Total operating revenues	857	855	974
Claims, Benefits and Expenses
Net incurred claims and benefits	492	479	488
Policyholders' dividends	0	0	0
Amortization of deferred acquisition costs	174	168	204
Other insurance related expenses	133	138	151
Other expenses	24	12	28
Total claims, benefits and expenses	823	797	871
Operating income (loss) from continuing operations before income tax	34	58	103
Income tax (expense) benefit on operating income (loss)	(13)	(21)	(34)
Net operating income (loss) from continuing operations	21	37	69
Net realized investment gains (losses), pre-tax	18	1	(1)
Income tax (expense) benefit on net realized investment gains (losses)	(3)	0	1
Net realized investment gains (losses), after tax	15	1	0
Net income (loss) from continuing operations	36	38	69
Life and Group Non-Core [Member]
Segment Reporting Information [Line Items]
Net written premiums	547	542	553
Operating Revenues
Net earned premiums	536	548	556
Net Investment Income	767	704	700
Other revenues	(2)	7	16
Total operating revenues	1,301	1,259	1,272
Claims, Benefits and Expenses
Net incurred claims and benefits	1,286	1,421	1,304
Policyholders' dividends	0	0	0
Amortization of deferred acquisition costs	0	314	28
Other insurance related expenses	132	142	130
Other expenses	8	11	30
Total claims, benefits and expenses	1,426	1,888	1,492
Operating income (loss) from continuing operations before income tax	(125)	(629)	(220)
Income tax (expense) benefit on operating income (loss)	145	315	151
Net operating income (loss) from continuing operations	20	(314)	(69)
Net realized investment gains (losses), pre-tax	25	(1)	7
Income tax (expense) benefit on net realized investment gains (losses)	(9)	9	0
Net realized investment gains (losses), after tax	16	8	7
Net income (loss) from continuing operations	36	(306)	(62)
Corporate and Other [Member]
Segment Reporting Information [Line Items]
Net written premiums	0	1	1
Operating Revenues
Net earned premiums	0	1	1
Net Investment Income	16	17	23
Other revenues	12	11	12
Total operating revenues	28	29	36
Claims, Benefits and Expenses
Net incurred claims and benefits	98	61	(29)
Policyholders' dividends	0	0	0
Amortization of deferred acquisition costs	0	0	0
Other insurance related expenses	(3)	(1)	1
Other expenses	209	186	210
Total claims, benefits and expenses	304	246	182
Operating income (loss) from continuing operations before income tax	(276)	(217)	(146)
Income tax (expense) benefit on operating income (loss)	98	80	54
Net operating income (loss) from continuing operations	(178)	(137)	(92)
Net realized investment gains (losses), pre-tax	(2)	13	20
Income tax (expense) benefit on net realized investment gains (losses)	1	(5)	(8)
Net realized investment gains (losses), after tax	(1)	8	12
Net income (loss) from continuing operations	(179)	(129)	(80)
Eliminations [Member]
Segment Reporting Information [Line Items]
Net written premiums	(1)	(2)	(2)
Operating Revenues
Net earned premiums	(1)	(2)	(2)
Net Investment Income	0	0	0
Other revenues	0	(3)	(5)
Total operating revenues	(1)	(5)	(7)
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	(1)	(2)	(2)
Other expenses	0	(3)	(5)
Total claims, benefits and expenses	(1)	(5)	(7)
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