Business Segments (Income Statement Information) (Details) - USD ($) $ in Millions	3 Months Ended
	Mar. 31, 2019	Mar. 31, 2018
Operating revenues
Net earned premiums	$ 1,803	$ 1,785
Net investment income	571	490
Non-insurance warranty revenue	281	238
Other revenues	9	10
Total operating revenues	2,664	2,523
Claims, Benefits and Expenses
Net incurred claims and benefits	1,351	1,333
Policyholders’ dividends	6	6
Amortization of deferred acquisition costs	342	296
Non-insurance warranty expense	260	216
Other insurance related expenses	251	277
Other expenses	66	61
Total claims, benefits and expenses	2,276	2,189
Core income (loss) before income tax	388	334
Income tax (expense) benefit on core income (loss)	(70)	(53)
Core income (loss)	318	281
Net investment gains (losses)	31	12
Income tax (expense) benefit on net investment gains (losses)	(7)	(2)
Net investment gains (losses), after tax	24	10
Net income	342	291
Operating Segments | Specialty
Operating revenues
Net earned premiums	661	672
Net investment income	155	122
Non-insurance warranty revenue	281	238
Other revenues	1	1
Total operating revenues	1,098	1,033
Claims, Benefits and Expenses
Net incurred claims and benefits	392	379
Policyholders’ dividends	1	1
Amortization of deferred acquisition costs	147	145
Non-insurance warranty expense	260	216
Other insurance related expenses	70	64
Other expenses	12	11
Total claims, benefits and expenses	882	816
Core income (loss) before income tax	216	217
Income tax (expense) benefit on core income (loss)	(47)	(46)
Core income (loss)	169	171
Operating Segments | Commercial
Operating revenues
Net earned premiums	763	743
Net investment income	190	149
Non-insurance warranty revenue	0	0
Other revenues	7	8
Total operating revenues	960	900
Claims, Benefits and Expenses
Net incurred claims and benefits	510	468
Policyholders’ dividends	5	5
Amortization of deferred acquisition costs	127	121
Non-insurance warranty expense	0	0
Other insurance related expenses	130	127
Other expenses	11	11
Total claims, benefits and expenses	783	732
Core income (loss) before income tax	177	168
Income tax (expense) benefit on core income (loss)	(38)	(35)
Core income (loss)	139	133
Operating Segments | International
Operating revenues
Net earned premiums	250	236
Net investment income	15	14
Non-insurance warranty revenue	0	0
Other revenues	0	0
Total operating revenues	265	250
Claims, Benefits and Expenses
Net incurred claims and benefits	162	142
Policyholders’ dividends	0	0
Amortization of deferred acquisition costs	68	30
Non-insurance warranty expense	0	0
Other insurance related expenses	25	56
Other expenses	4	(4)
Total claims, benefits and expenses	259	224
Core income (loss) before income tax	6	26
Income tax (expense) benefit on core income (loss)	0	(3)
Core income (loss)	6	23
Operating Segments | Life & Group
Operating revenues
Net earned premiums	130	134
Net investment income	204	200
Non-insurance warranty revenue	0	0
Other revenues	1	1
Total operating revenues	335	335
Claims, Benefits and Expenses
Net incurred claims and benefits	308	303
Policyholders’ dividends	0	0
Amortization of deferred acquisition costs	0	0
Non-insurance warranty expense	0	0
Other insurance related expenses	28	30
Other expenses	2	2
Total claims, benefits and expenses	338	335
Core income (loss) before income tax	(3)	0
Income tax (expense) benefit on core income (loss)	13	14
Core income (loss)	10	14
Operating Segments | Corporate & Other
Operating revenues
Net earned premiums	0	0
Net investment income	7	5
Non-insurance warranty revenue	0	0
Other revenues	2	1
Total operating revenues	9	6
Claims, Benefits and Expenses
Net incurred claims and benefits	(21)	41
Policyholders’ dividends	0	0
Amortization of deferred acquisition costs	0	0
Non-insurance warranty expense	0	0
Other insurance related expenses	(1)	0
Other expenses	39	42
Total claims, benefits and expenses	17	83
Core income (loss) before income tax	(8)	(77)
Income tax (expense) benefit on core income (loss)	2	17
Core income (loss)	(6)	(60)
Eliminations
Operating revenues
Net earned premiums	(1)	0
Net investment income	0	0
Non-insurance warranty revenue	0	0
Other revenues	(2)	(1)
Total operating revenues	(3)	(1)
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	(1)	0
Other expenses	(2)	(1)
Total claims, benefits and expenses	(3)	(1)
Core income (loss) before income tax	0	0
Income tax (expense) benefit on core income (loss)	0	0
Core income (loss)	$ 0	$ 0