Investments (Details) (USD $) In Millions, unless otherwise specified	Mar. 31, 2015	Dec. 31, 2014
Available-for-sale securities
Amortized cost, fixed maturities	$ 9,499
Amortized cost	10,286	9,907
Gross unrealized gains	660	584
Gross unrealized losses	29	45
Estimated fair value, fixed maturities	10,055	9,571
Estimated fair value, equity securities	862	875
Estimated fair value	10,917us-gaap_AvailableForSaleSecurities	10,446us-gaap_AvailableForSaleSecurities
Indemnity
Available-for-sale securities
Amortized cost, fixed maturities	545	555
Amortized cost, equity securities	24	24
Amortized cost	569	579
Gross unrealized gains	15	14
Gross unrealized losses	3	4
Estimated fair value, fixed maturities	556	564
Estimated fair value, equity securities	25	25
Estimated fair value	581	589
Indemnity \| Fixed maturities
Available-for-sale securities
Amortized cost, fixed maturities	545	555
Gross unrealized gains, fixed maturities	14	13
Gross unrealized losses, fixed maturities	3	4
Estimated fair value, fixed maturities	556	564
Indemnity \| States & political subdivisions
Available-for-sale securities
Amortized cost, fixed maturities	213	219
Gross unrealized gains, fixed maturities	12	12
Gross unrealized losses, fixed maturities	0	0
Estimated fair value, fixed maturities	225	231
Indemnity \| Corporate debt securities
Available-for-sale securities
Amortized cost, fixed maturities	232	236
Gross unrealized gains, fixed maturities	2	1
Gross unrealized losses, fixed maturities	2	3
Estimated fair value, fixed maturities	232	234
Indemnity \| Residential mortgage-backed securities
Available-for-sale securities
Amortized cost, fixed maturities	8	8
Gross unrealized gains, fixed maturities	0	0
Gross unrealized losses, fixed maturities	0	0
Estimated fair value, fixed maturities	8	8
Indemnity \| Commercial mortgage-backed securities
Available-for-sale securities
Amortized cost, fixed maturities	51	52
Gross unrealized gains, fixed maturities	0	0
Gross unrealized losses, fixed maturities	1	1
Estimated fair value, fixed maturities	50	51
Indemnity \| Collateralized debt obligations
Available-for-sale securities
Amortized cost, fixed maturities	36	33
Gross unrealized gains, fixed maturities	0	0
Gross unrealized losses, fixed maturities	0	0
Estimated fair value, fixed maturities	36	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	11	11
Gross unrealized gains, equity securities	1	1
Gross unrealized losses, equity securities	0	0
Estimated fair value, equity securities	12	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	0	0
Estimated fair value, equity securities	13	13
Exchange
Available-for-sale securities
Amortized cost, fixed maturities	8,954	8,540
Amortized cost, equity securities	763	788
Amortized cost	9,717	9,328
Gross unrealized gains	645	570
Gross unrealized losses	26	41
Estimated fair value, fixed maturities	9,499	9,007
Estimated fair value, equity securities	837	850
Estimated fair value	10,336	9,857
Exchange \| Fixed maturities
Available-for-sale securities
Amortized cost, fixed maturities	8,954	8,540
Gross unrealized gains, fixed maturities	570	503
Gross unrealized losses, fixed maturities	25	36
Estimated fair value, fixed maturities	9,499	9,007
Exchange \| U.S. treasury
Available-for-sale securities
Amortized cost, fixed maturities	6	6
Gross unrealized gains, fixed maturities	0	0
Gross unrealized losses, fixed maturities	0	0
Estimated fair value, fixed maturities	6	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	1,421	1,394
Gross unrealized gains, fixed maturities	86	84
Gross unrealized losses, fixed maturities	1	1
Estimated fair value, fixed maturities	1,506	1,477
Exchange \| Foreign government securities
Available-for-sale securities
Amortized cost, fixed maturities	80	10
Gross unrealized gains, fixed maturities	2	0
Gross unrealized losses, fixed maturities	0	0
Estimated fair value, fixed maturities	82	10
Exchange \| Corporate debt securities
Available-for-sale securities
Amortized cost, fixed maturities	7,278	6,918
Gross unrealized gains, fixed maturities	470	405
Gross unrealized losses, fixed maturities	24	34
Estimated fair value, fixed maturities	7,724	7,289
Exchange \| Residential mortgage-backed securities
Available-for-sale securities
Amortized cost, fixed maturities	57	109
Gross unrealized gains, fixed maturities	1	3
Gross unrealized losses, fixed maturities	0	1
Estimated fair value, fixed maturities	58	111
Exchange \| Commercial mortgage-backed securities
Available-for-sale securities
Amortized cost, fixed maturities	28	28
Gross unrealized gains, fixed maturities	2	2
Gross unrealized losses, fixed maturities	0	0
Estimated fair value, fixed maturities	30	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	75	66
Gross unrealized gains, fixed maturities	3	3
Gross unrealized losses, fixed maturities	0	0
Estimated fair value, fixed maturities	78	69
Exchange \| Nonredeemable preferred stock
Available-for-sale securities
Amortized cost, equity securities	667	650
Gross unrealized gains, equity securities	72	64
Gross unrealized losses, equity securities	1	4
Estimated fair value, equity securities	738	710
Exchange \| Common stock
Available-for-sale securities
Amortized cost, equity securities	96	138
Gross unrealized gains, equity securities	3	3
Gross unrealized losses, equity securities	0	1
Estimated fair value, equity securities	$ 99	$ 140

Amount before tax of unrealized gain in accumulated other comprehensive income (AOCI) on investments in debt securities classified as available-for-sale.

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