Business Segments (Income Statement Information) (Details) - USD ($) $ in Millions	3 Months Ended		6 Months Ended
	Jun. 30, 2019	Jun. 30, 2018	Jun. 30, 2019	Jun. 30, 2018
Operating revenues
Net earned premiums	$ 1,824	$ 1,815	$ 3,627	$ 3,600
Net investment income	515	506	1,086	996
Non-insurance warranty revenue	285	248	566	486
Other revenues	4	6	13	16
Total operating revenues	2,628	2,575	5,292	5,098
Claims, Benefits and Expenses
Net incurred claims and benefits	1,346	1,321	2,697	2,654
Policyholders’ dividends	6	6	12	12
Amortization of deferred acquisition costs	338	359	680	655
Non-insurance warranty expense	263	225	523	441
Other insurance related expenses	258	236	509	513
Other expenses	57	97	123	158
Total claims, benefits and expenses	2,268	2,244	4,544	4,433
Core income (loss) before income tax	360	331	748	665
Income tax (expense) benefit on core income (loss)	(66)	(61)	(136)	(114)
Core income (loss)	294	270	612	551
Net investment gains (losses)	(18)	(1)	13	11
Income tax (expense) benefit on net investment gains (losses)	2	1	(5)	(1)
Net investment gains (losses), after tax	(16)	0	8	10
Net income	278	270	620	561
Operating Segments | Specialty
Operating revenues
Net earned premiums	688	683	1,349	1,355
Net investment income	134	130	289	252
Non-insurance warranty revenue	285	248	566	486
Other revenues	(1)	0	0	1
Total operating revenues	1,106	1,061	2,204	2,094
Claims, Benefits and Expenses
Net incurred claims and benefits	395	372	787	751
Policyholders’ dividends	1	1	2	2
Amortization of deferred acquisition costs	152	149	299	294
Non-insurance warranty expense	263	225	523	441
Other insurance related expenses	76	70	146	134
Other expenses	12	12	24	23
Total claims, benefits and expenses	899	829	1,781	1,645
Core income (loss) before income tax	207	232	423	449
Income tax (expense) benefit on core income (loss)	(46)	(49)	(93)	(95)
Core income (loss)	161	183	330	354
Operating Segments | Commercial
Operating revenues
Net earned premiums	763	753	1,526	1,496
Net investment income	154	157	344	306
Non-insurance warranty revenue	0	0	0	0
Other revenues	3	8	10	16
Total operating revenues	920	918	1,880	1,818
Claims, Benefits and Expenses
Net incurred claims and benefits	507	470	1,017	938
Policyholders’ dividends	5	5	10	10
Amortization of deferred acquisition costs	130	127	257	248
Non-insurance warranty expense	0	0	0	0
Other insurance related expenses	119	126	249	253
Other expenses	7	10	18	21
Total claims, benefits and expenses	768	738	1,551	1,470
Core income (loss) before income tax	152	180	329	348
Income tax (expense) benefit on core income (loss)	(32)	(37)	(70)	(72)
Core income (loss)	120	143	259	276
Operating Segments | International
Operating revenues
Net earned premiums	243	248	493	484
Net investment income	15	15	30	29
Non-insurance warranty revenue	0	0	0	0
Other revenues	1	(1)	1	(1)
Total operating revenues	259	262	524	512
Claims, Benefits and Expenses
Net incurred claims and benefits	147	166	309	308
Policyholders’ dividends	0	0	0	0
Amortization of deferred acquisition costs	56	83	124	113
Non-insurance warranty expense	0	0	0	0
Other insurance related expenses	34	10	59	66
Other expenses	3	7	7	3
Total claims, benefits and expenses	240	266	499	490
Core income (loss) before income tax	19	(4)	25	22
Income tax (expense) benefit on core income (loss)	(2)	(3)	(2)	(6)
Core income (loss)	17	(7)	23	16
Operating Segments | Life & Group
Operating revenues
Net earned premiums	130	131	260	265
Net investment income	205	198	409	398
Non-insurance warranty revenue	0	0	0	0
Other revenues	0	0	1	1
Total operating revenues	335	329	670	664
Claims, Benefits and Expenses
Net incurred claims and benefits	309	327	617	630
Policyholders’ dividends	0	0	0	0
Amortization of deferred acquisition costs	0	0	0	0
Non-insurance warranty expense	0	0	0	0
Other insurance related expenses	30	30	58	60
Other expenses	2	1	4	3
Total claims, benefits and expenses	341	358	679	693
Core income (loss) before income tax	(6)	(29)	(9)	(29)
Income tax (expense) benefit on core income (loss)	13	19	26	33
Core income (loss)	7	(10)	17	4
Operating Segments | Corporate & Other
Operating revenues
Net earned premiums	0	0	0	0
Net investment income	7	6	14	11
Non-insurance warranty revenue	0	0	0	0
Other revenues	2	(1)	4	0
Total operating revenues	9	5	18	11
Claims, Benefits and Expenses
Net incurred claims and benefits	(12)	(14)	(33)	27
Policyholders’ dividends	0	0	0	0
Amortization of deferred acquisition costs	0	0	0	0
Non-insurance warranty expense	0	0	0	0
Other insurance related expenses	(1)	0	(2)	0
Other expenses	34	67	73	109
Total claims, benefits and expenses	21	53	38	136
Core income (loss) before income tax	(12)	(48)	(20)	(125)
Income tax (expense) benefit on core income (loss)	1	9	3	26
Core income (loss)	(11)	(39)	(17)	(99)
Eliminations
Operating revenues
Net earned premiums	0	0	(1)	0
Net investment income	0	0	0	0
Non-insurance warranty revenue	0	0	0	0
Other revenues	(1)	0	(3)	(1)
Total operating revenues	(1)	0	(4)	(1)
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
Non-insurance warranty expense	0	0	0	0
Other insurance related expenses	0	0	(1)	0
Other expenses	(1)	0	(3)	(1)
Total claims, benefits and expenses	(1)	0	(4)	(1)
Core income (loss) before income tax	0	0	0	0
Income tax (expense) benefit on core income (loss)	0	0	0	0
Core income (loss)	$ 0	$ 0	$ 0	$ 0