Business Segments (Income Statement Information) (Details) - USD ($) $ in Millions	3 Months Ended		9 Months Ended
	Sep. 30, 2019	Sep. 30, 2018	Sep. 30, 2019	Sep. 30, 2018
Operating revenues
Net earned premiums	$ 1,890	$ 1,853	$ 5,517	$ 5,453
Net investment income	487	487	1,573	1,483
Non-insurance warranty revenue	292	258	858	744
Other revenues	9	10	22	26
Total operating revenues	2,678	2,608	7,970	7,706
Claims, Benefits and Expenses
Net incurred claims and benefits	1,607	1,306	4,304	3,960
Policyholders’ dividends	7	6	19	18
Amortization of deferred acquisition costs	345	337	1,025	992
Non-insurance warranty expense	278	235	801	676
Other insurance related expenses	257	266	766	779
Other expenses	64	70	187	228
Total claims, benefits and expenses	2,558	2,220	7,102	6,653
Core income (loss) before income tax	120	388	868	1,053
Income tax (expense) benefit on core income (loss)	(18)	(71)	(154)	(185)
Core income (loss)	102	317	714	868
Net investment gains (losses)	7	14	20	25
Income tax (expense) benefit on net investment gains (losses)	(2)	(1)	(7)	(2)
Net investment gains (losses), after tax	5	13	13	23
Deferred Income Tax Expense (Benefit), Remeasurement of Deferred Tax Asset		6		6
Net income	107	336	727	897
Operating Segments | Specialty
Operating revenues
Net earned premiums	712	684	2,061	2,039
Net investment income	121	124	410	376
Non-insurance warranty revenue	292	258	858	744
Other revenues	1	0	1	1
Total operating revenues	1,126	1,066	3,330	3,160
Claims, Benefits and Expenses
Net incurred claims and benefits	411	373	1,198	1,124
Policyholders’ dividends	2	1	4	3
Amortization of deferred acquisition costs	155	153	454	447
Non-insurance warranty expense	278	235	801	676
Other insurance related expenses	71	68	217	202
Other expenses	13	11	37	34
Total claims, benefits and expenses	930	841	2,711	2,486
Core income (loss) before income tax	196	225	619	674
Income tax (expense) benefit on core income (loss)	(43)	(48)	(136)	(143)
Core income (loss)	153	177	483	531
Operating Segments | Commercial
Operating revenues
Net earned premiums	813	782	2,339	2,278
Net investment income	136	144	480	450
Non-insurance warranty revenue	0	0	0	0
Other revenues	10	8	20	24
Total operating revenues	959	934	2,839	2,752
Claims, Benefits and Expenses
Net incurred claims and benefits	564	496	1,581	1,434
Policyholders’ dividends	5	5	15	15
Amortization of deferred acquisition costs	134	127	391	375
Non-insurance warranty expense	0	0	0	0
Other insurance related expenses	123	133	372	386
Other expenses	9	10	27	31
Total claims, benefits and expenses	835	771	2,386	2,241
Core income (loss) before income tax	124	163	453	511
Income tax (expense) benefit on core income (loss)	(27)	(36)	(97)	(108)
Core income (loss)	97	127	356	403
Operating Segments | International
Operating revenues
Net earned premiums	236	255	729	739
Net investment income	17	14	47	43
Non-insurance warranty revenue	0	0	0	0
Other revenues	(1)	1	0	0
Total operating revenues	252	270	776	782
Claims, Benefits and Expenses
Net incurred claims and benefits	163	172	472	480
Policyholders’ dividends	0	0	0	0
Amortization of deferred acquisition costs	56	57	180	170
Non-insurance warranty expense	0	0	0	0
Other insurance related expenses	35	36	94	102
Other expenses	7	3	14	6
Total claims, benefits and expenses	261	268	760	758
Core income (loss) before income tax	(9)	2	16	24
Income tax (expense) benefit on core income (loss)	0	(1)	(2)	(7)
Core income (loss)	(9)	1	14	17
Operating Segments | Life & Group
Operating revenues
Net earned premiums	130	133	390	398
Net investment income	207	200	616	598
Non-insurance warranty revenue	0	0	0	0
Other revenues	(1)	(1)	0	0
Total operating revenues	336	332	1,006	996
Claims, Benefits and Expenses
Net incurred claims and benefits	476	277	1,093	907
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	29	31	87	91
Other expenses	1	2	5	5
Total claims, benefits and expenses	506	310	1,185	1,003
Core income (loss) before income tax	(170)	22	(179)	(7)
Income tax (expense) benefit on core income (loss)	48	10	74	43
Core income (loss)	(122)	32	(105)	36
Operating Segments | Corporate & Other
Operating revenues
Net earned premiums	0	0	0	0
Net investment income	6	5	20	16
Non-insurance warranty revenue	0	0	0	0
Other revenues	1	2	5	2
Total operating revenues	7	7	25	18
Claims, Benefits and Expenses
Net incurred claims and benefits	(7)	(12)	(40)	15
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	(1)	(2)	(1)
Other expenses	35	44	108	153
Total claims, benefits and expenses	28	31	66	167
Core income (loss) before income tax	(21)	(24)	(41)	(149)
Income tax (expense) benefit on core income (loss)	4	4	7	30
Core income (loss)	(17)	(20)	(34)	(119)
Eliminations
Operating revenues
Net earned premiums	(1)	(1)	(2)	(1)
Net investment income	0	0	0	0
Non-insurance warranty revenue	0	0	0	0
Other revenues	(1)	0	(4)	(1)
Total operating revenues	(2)	(1)	(6)	(2)
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	(1)	(1)	(2)	(1)
Other expenses	(1)	0	(4)	(1)
Total claims, benefits and expenses	(2)	(1)	(6)	(2)
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