Investments (Details) - USD ($) $ in Millions	Sep. 30, 2015	Dec. 31, 2014
Available-for-sale securities
Amortized cost, fixed maturities	$ 9,687
Amortized cost	10,388	$ 9,907
Gross unrealized gains	457	584
Gross unrealized losses	125	45
Estimated fair value, fixed maturities	9,980	9,571
Estimated fair value, equity securities	740	875
Estimated fair value	10,720	10,446
Indemnity
Available-for-sale securities
Amortized cost, fixed maturities	581	555
Amortized cost, equity securities	20	24
Amortized cost	601	579
Gross unrealized gains	13	14
Gross unrealized losses	6	4
Estimated fair value, fixed maturities	588	564
Estimated fair value, equity securities	20	25
Estimated fair value	608	589
Indemnity \| Fixed maturities
Available-for-sale securities
Amortized cost, fixed maturities	581	555
Gross unrealized gains, fixed maturities	12	13
Gross unrealized losses, fixed maturities	5	4
Estimated fair value, fixed maturities	588	564
Indemnity \| States & political subdivisions
Available-for-sale securities
Amortized cost, fixed maturities	226	219
Gross unrealized gains, fixed maturities	11	12
Gross unrealized losses, fixed maturities	0	0
Estimated fair value, fixed maturities	237	231
Indemnity \| Corporate debt securities
Available-for-sale securities
Amortized cost, fixed maturities	248	236
Gross unrealized gains, fixed maturities	1	1
Gross unrealized losses, fixed maturities	4	3
Estimated fair value, fixed maturities	245	234
Indemnity \| Residential mortgage-backed securities
Available-for-sale securities
Amortized cost, fixed maturities	11	8
Gross unrealized gains, fixed maturities	0	0
Gross unrealized losses, fixed maturities	0	0
Estimated fair value, fixed maturities	11	8
Indemnity \| Commercial mortgage-backed securities
Available-for-sale securities
Amortized cost, fixed maturities	45	52
Gross unrealized gains, fixed maturities	0	0
Gross unrealized losses, fixed maturities	1	1
Estimated fair value, fixed maturities	44	51
Indemnity \| Collateralized debt obligations
Available-for-sale securities
Amortized cost, fixed maturities	46	33
Gross unrealized gains, fixed maturities	0	0
Gross unrealized losses, fixed maturities	0	0
Estimated fair value, fixed maturities	46	33
Indemnity \| Other debt securities
Available-for-sale securities
Amortized cost, fixed maturities	5	7
Gross unrealized gains, fixed maturities	0	0
Gross unrealized losses, fixed maturities	0	0
Estimated fair value, fixed maturities	5	7
Indemnity \| Nonredeemable preferred stock
Available-for-sale securities
Amortized cost, equity securities	7	11
Gross unrealized gains, equity securities	1	1
Gross unrealized losses, equity securities	0	0
Estimated fair value, equity securities	8	12
Indemnity \| Common stock
Available-for-sale securities
Amortized cost, equity securities	13	13
Gross unrealized gains, equity securities	0	0
Gross unrealized losses, equity securities	1	0
Estimated fair value, equity securities	12	13
Exchange
Available-for-sale securities
Amortized cost, fixed maturities	9,106	8,540
Amortized cost, equity securities	681	788
Amortized cost	9,787	9,328
Gross unrealized gains	444	570
Gross unrealized losses	119	41
Estimated fair value, fixed maturities	9,392	9,007
Estimated fair value, equity securities	720	850
Estimated fair value	10,112	9,857
Exchange \| Fixed maturities
Available-for-sale securities
Amortized cost, fixed maturities	9,106	8,540
Gross unrealized gains, fixed maturities	399	503
Gross unrealized losses, fixed maturities	113	36
Estimated fair value, fixed maturities	9,392	9,007
Exchange \| U.S. treasury
Available-for-sale securities
Amortized cost, fixed maturities	8	6
Gross unrealized gains, fixed maturities	0	0
Gross unrealized losses, fixed maturities	0	0
Estimated fair value, fixed maturities	8	6
Exchange \| Government sponsored enterprises
Available-for-sale securities
Amortized cost, fixed maturities	3	3
Gross unrealized gains, fixed maturities	1	1
Gross unrealized losses, fixed maturities	0	0
Estimated fair value, fixed maturities	4	4
Exchange \| States & political subdivisions
Available-for-sale securities
Amortized cost, fixed maturities	1,402	1,394
Gross unrealized gains, fixed maturities	75	84
Gross unrealized losses, fixed maturities	1	1
Estimated fair value, fixed maturities	1,476	1,477
Exchange \| Foreign government securities
Available-for-sale securities
Amortized cost, fixed maturities	91	10
Gross unrealized gains, fixed maturities	0	0
Gross unrealized losses, fixed maturities	5	0
Estimated fair value, fixed maturities	86	10
Exchange \| Corporate debt securities
Available-for-sale securities
Amortized cost, fixed maturities	7,450	6,918
Gross unrealized gains, fixed maturities	314	405
Gross unrealized losses, fixed maturities	107	34
Estimated fair value, fixed maturities	7,657	7,289
Exchange \| Residential mortgage-backed securities
Available-for-sale securities
Amortized cost, fixed maturities	30	109
Gross unrealized gains, fixed maturities	0	3
Gross unrealized losses, fixed maturities	0	1
Estimated fair value, fixed maturities	30	111
Exchange \| Commercial mortgage-backed securities
Available-for-sale securities
Amortized cost, fixed maturities	28	28
Gross unrealized gains, fixed maturities	1	2
Gross unrealized losses, fixed maturities	0	0
Estimated fair value, fixed maturities	29	30
Exchange \| Collateralized debt obligations
Available-for-sale securities
Amortized cost, fixed maturities	6	6
Gross unrealized gains, fixed maturities	5	5
Gross unrealized losses, fixed maturities	0	0
Estimated fair value, fixed maturities	11	11
Exchange \| Other debt securities
Available-for-sale securities
Amortized cost, fixed maturities	88	66
Gross unrealized gains, fixed maturities	3	3
Gross unrealized losses, fixed maturities	0	0
Estimated fair value, fixed maturities	91	69
Exchange \| Nonredeemable preferred stock
Available-for-sale securities
Amortized cost, equity securities	585	650
Gross unrealized gains, equity securities	43	64
Gross unrealized losses, equity securities	5	4
Estimated fair value, equity securities	623	710
Exchange \| Common stock
Available-for-sale securities
Amortized cost, equity securities	96	138
Gross unrealized gains, equity securities	2	3
Gross unrealized losses, equity securities	1	1
Estimated fair value, equity securities	$ 97	$ 140

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