Business Segments (Income Statement Information) (Details) - USD ($) $ in Millions	3 Months Ended
	Mar. 31, 2018	Mar. 31, 2017
Operating revenues
Net earned premiums	$ 1,785	$ 1,645
Net investment income	490	545
Non-insurance warranty revenue	238	93
Other revenues	10	11
Total operating revenues	2,523	2,294
Claims, Benefits and Expenses
Net incurred claims and benefits	1,333	1,289
Policyholders’ dividends	6	4
Amortization of deferred acquisition costs	296	305
Non-insurance warranty expense	216	70
Other insurance related expenses	277	254
Other expenses	61	65
Total claims, benefits and expenses	2,189	1,987
Core income (loss) before income tax	334	307
Income tax (expense) benefit on core income (loss)	(53)	(72)
Core income (loss)	281	235
Net realized investment gains (losses)	12	36
Income tax (expense) benefit on net realized investment gains (losses)	(2)	(11)
Net realized investment gains (losses), after tax	10	25
Net income	291	260
Operating Segments | Specialty
Operating revenues
Net earned premiums	672	654
Net investment income	122	148
Non-insurance warranty revenue	238	93
Other revenues	1	1
Total operating revenues	1,033	896
Claims, Benefits and Expenses
Net incurred claims and benefits	379	400
Policyholders’ dividends	1	1
Amortization of deferred acquisition costs	145	142
Non-insurance warranty expense	216	70
Other insurance related expenses	64	67
Other expenses	11	10
Total claims, benefits and expenses	816	690
Core income (loss) before income tax	217	206
Income tax (expense) benefit on core income (loss)	(46)	(69)
Core income (loss)	171	137
Operating Segments | Commercial
Operating revenues
Net earned premiums	743	661
Net investment income	149	183
Non-insurance warranty revenue	0	0
Other revenues	8	9
Total operating revenues	900	853
Claims, Benefits and Expenses
Net incurred claims and benefits	468	423
Policyholders’ dividends	5	3
Amortization of deferred acquisition costs	121	117
Non-insurance warranty expense	0	0
Other insurance related expenses	127	128
Other expenses	11	15
Total claims, benefits and expenses	732	686
Core income (loss) before income tax	168	167
Income tax (expense) benefit on core income (loss)	(35)	(56)
Core income (loss)	133	111
Operating Segments | International
Operating revenues
Net earned premiums	236	197
Net investment income	14	12
Non-insurance warranty revenue	0	0
Other revenues	0	0
Total operating revenues	250	209
Claims, Benefits and Expenses
Net incurred claims and benefits	142	115
Policyholders’ dividends	0	0
Amortization of deferred acquisition costs	30	46
Non-insurance warranty expense	0	0
Other insurance related expenses	56	27
Other expenses	(4)	(6)
Total claims, benefits and expenses	224	182
Core income (loss) before income tax	26	27
Income tax (expense) benefit on core income (loss)	(3)	(7)
Core income (loss)	23	20
Operating Segments | Life & Group revenues
Operating revenues
Net earned premiums	134	133
Net investment income	200	197
Non-insurance warranty revenue	0	0
Other revenues	1	1
Total operating revenues	335	331
Claims, Benefits and Expenses
Net incurred claims and benefits	303	330
Policyholders’ dividends	0	0
Amortization of deferred acquisition costs	0	0
Non-insurance warranty expense	0	0
Other insurance related expenses	30	32
Other expenses	2	2
Total claims, benefits and expenses	335	364
Core income (loss) before income tax	0	(33)
Income tax (expense) benefit on core income (loss)	14	37
Core income (loss)	14	4
Operating Segments | Corporate & Other revenues
Operating revenues
Net earned premiums	0	0
Net investment income	5	5
Non-insurance warranty revenue	0	0
Other revenues	1	0
Total operating revenues	6	5
Claims, Benefits and Expenses
Net incurred claims and benefits	41	21
Policyholders’ dividends	0	0
Amortization of deferred acquisition costs	0	0
Non-insurance warranty expense	0	0
Other insurance related expenses	0	0
Other expenses	42	44
Total claims, benefits and expenses	83	65
Core income (loss) before income tax	(77)	(60)
Income tax (expense) benefit on core income (loss)	17	23
Core income (loss)	(60)	(37)
Eliminations
Operating revenues
Net earned premiums	0	0
Net investment income	0	0
Non-insurance warranty revenue	0	0
Other revenues	(1)	0
Total operating revenues	(1)	0
Claims, Benefits and Expenses
Net incurred claims and benefits	0	0
Policyholders’ dividends	0	0
Amortization of deferred acquisition costs	0	0
Non-insurance warranty expense	0	0
Other insurance related expenses	0	0
Other expenses	(1)	0
Total claims, benefits and expenses	(1)	0
Core income (loss) before income tax	0	0
Income tax (expense) benefit on core income (loss)	0	0
Core income (loss)	$ 0	$ 0