Business Segments (Income Statement Information) (Details) - USD ($) $ in Millions	3 Months Ended		9 Months Ended
	Sep. 30, 2016	Sep. 30, 2015	Sep. 30, 2016	Sep. 30, 2015
Operating Revenues
Net earned premiums	$ 1,767	$ 1,751	$ 5,196	$ 5,173
Net investment income	524	354	1,461	1,412
Other revenues	96	97	293	286
Total operating revenues	2,387	2,202	6,950	6,871
Claims, Benefits and Expenses
Net incurred claims and benefits	1,195	1,198	3,934	3,999
Policyholders' dividends	7	2	15	9
Amortization of deferred acquisition costs	314	319	926	936
Other insurance related expenses	295	263	842	790
Other expenses	147	138	439	388
Total claims, benefits and expenses	1,958	1,920	6,156	6,122
Operating income (loss) before income tax	429	282	794	749
Income tax (expense) benefit on operating income (loss)	(118)	(72)	(191)	(182)
Net operating income (loss)	311	210	603	567
Net realized investment gains (losses), pre-tax	46	(49)	26	(39)
Income tax (expense) benefit on net realized investment gains (losses)	(14)	17	(11)	21
Net realized investment gains (losses), after tax	32	(32)	15	(18)
Net Income (Loss)	343	178	618	549
Specialty [Member]
Operating Revenues
Net earned premiums	704	706	2,088	2,075
Net investment income	140	76	380	365
Other revenues	93	86	269	245
Total operating revenues	937	868	2,737	2,685
Claims, Benefits and Expenses
Net incurred claims and benefits	330	307	1,097	1,152
Policyholders' dividends	4	1	6	3
Amortization of deferred acquisition costs	151	150	443	440
Other insurance related expenses	77	67	225	202
Other expenses	78	73	232	209
Total claims, benefits and expenses	640	598	2,003	2,006
Operating income (loss) before income tax	297	270	734	679
Income tax (expense) benefit on operating income (loss)	(102)	(91)	(248)	(228)
Net operating income (loss)	195	179	486	451
Net realized investment gains (losses), pre-tax	9	(22)	2	(18)
Income tax (expense) benefit on net realized investment gains (losses)	(3)	8	(1)	7
Net realized investment gains (losses), after tax	6	(14)	1	(11)
Net Income (Loss)	201	165	487	440
Commercial [Member]
Operating Revenues
Net earned premiums	719	705	2,103	2,086
Net investment income	175	82	465	455
Other revenues	7	9	21	27
Total operating revenues	901	796	2,589	2,568
Claims, Benefits and Expenses
Net incurred claims and benefits	446	427	1,357	1,388
Policyholders' dividends	3	1	9	6
Amortization of deferred acquisition costs	118	118	351	352
Other insurance related expenses	151	128	422	385
Other expenses	9	10	25	23
Total claims, benefits and expenses	727	684	2,164	2,154
Operating income (loss) before income tax	174	112	425	414
Income tax (expense) benefit on operating income (loss)	(60)	(37)	(145)	(141)
Net operating income (loss)	114	75	280	273
Net realized investment gains (losses), pre-tax	12	(29)	2	(23)
Income tax (expense) benefit on net realized investment gains (losses)	(3)	8	0	7
Net realized investment gains (losses), after tax	9	(21)	2	(16)
Net Income (Loss)	123	54	282	257
International [Member]
Operating Revenues
Net earned premiums	210	203	605	601
Net investment income	13	13	38	40
Other revenues	0	1	1	0
Total operating revenues	223	217	644	641
Claims, Benefits and Expenses
Net incurred claims and benefits	117	106	395	336
Policyholders' dividends	0	0	0	0
Amortization of deferred acquisition costs	45	45	132	125
Other insurance related expenses	33	33	98	101
Other expenses	1	9	17	9
Total claims, benefits and expenses	196	193	642	571
Operating income (loss) before income tax	27	24	2	70
Income tax (expense) benefit on operating income (loss)	(7)	(15)	(3)	(30)
Net operating income (loss)	20	9	(1)	40
Net realized investment gains (losses), pre-tax	6	(1)	14	1
Income tax (expense) benefit on net realized investment gains (losses)	(1)	1	(3)	0
Net realized investment gains (losses), after tax	5	0	11	1
Net Income (Loss)	25	9	10	41
Life and Group Non-Core [Member]
Operating Revenues
Net earned premiums	134	137	401	412
Net investment income	192	182	567	540
Other revenues	(4)	(1)	(1)	8
Total operating revenues	322	318	967	960
Claims, Benefits and Expenses
Net incurred claims and benefits	313	361	976	1,045
Policyholders' dividends	0	0	0	0
Amortization of deferred acquisition costs	0	6	0	19
Other insurance related expenses	37	35	101	104
Other expenses	2	1	7	10
Total claims, benefits and expenses	352	403	1,084	1,178
Operating income (loss) before income tax	(30)	(85)	(117)	(218)
Income tax (expense) benefit on operating income (loss)	36	55	117	147
Net operating income (loss)	6	(30)	0	(71)
Net realized investment gains (losses), pre-tax	17	2	12	(2)
Income tax (expense) benefit on net realized investment gains (losses)	(6)	0	(9)	8
Net realized investment gains (losses), after tax	11	2	3	6
Net Income (Loss)	17	(28)	3	(65)
Corporate and Other Non-Core [Member]
Operating Revenues
Net earned premiums	0	0	0	0
Net investment income	4	1	11	12
Other revenues	0	4	3	9
Total operating revenues	4	5	14	21
Claims, Benefits and Expenses
Net incurred claims and benefits	(11)	(3)	109	78
Policyholders' dividends	0	0	0	0
Amortization of deferred acquisition costs	0	0	0	0
Other insurance related expenses	(3)	0	(3)	(1)
Other expenses	57	47	158	140
Total claims, benefits and expenses	43	44	264	217
Operating income (loss) before income tax	(39)	(39)	(250)	(196)
Income tax (expense) benefit on operating income (loss)	15	16	88	70
Net operating income (loss)	(24)	(23)	(162)	(126)
Net realized investment gains (losses), pre-tax	2	1	(4)	3
Income tax (expense) benefit on net realized investment gains (losses)	(1)	0	2	(1)
Net realized investment gains (losses), after tax	1	1	(2)	2
Net Income (Loss)	(23)	(22)	(164)	(124)
Eliminations [Member]
Operating Revenues
Net earned premiums	0	0	(1)	(1)
Net investment income	0	0	0	0
Other revenues	0	(2)	0	(3)
Total operating revenues	0	(2)	(1)	(4)
Claims, Benefits and Expenses
Net incurred claims and benefits	0	0	0	0
Policyholders' dividends	0	0	0	0
Amortization of deferred acquisition costs	0	0	0	0
Other insurance related expenses	0	0	(1)	(1)
Other expenses	0	(2)	0	(3)
Total claims, benefits and expenses	0	(2)	(1)	(4)
Operating income (loss) before income tax	0	0	0	0
Income tax (expense) benefit on operating income (loss)	0	0	0	0
Net operating income (loss)	0	0	0	0
Net realized investment gains (losses), pre-tax	0	0	0	0
Income tax (expense) benefit on net realized investment gains (losses)	0	0	0	0
Net realized investment gains (losses), after tax	0	0	0	0
Net Income (Loss)	$ 0	$ 0	$ 0	$ 0