Investments (Details) (USD $) In Millions, unless otherwise specified	Dec. 31, 2013	Dec. 31, 2012
Available-for-sale securities
Amortized cost	$ 9,147	$ 8,378
Gross unrealized gains	492	790
Gross unrealized losses	82	9
Estimated fair value, fixed maturities	8,688	8,159
Estimated fair value, equity securities	869	1,000
Estimated fair value	9,557	9,159
Indemnity
Available-for-sale securities
Amortized cost, fixed maturities	518	437
Amortized cost, equity securities	50	54
Amortized cost	568	491
Gross unrealized gains	11	17
Gross unrealized losses	3	1
Estimated fair value, fixed maturities	526	452
Estimated fair value, equity securities	50	55
Estimated fair value	576	507
Indemnity | Fixed maturities
Available-for-sale securities
Amortized cost, fixed maturities	518	437
Gross unrealized gains	9	15
Gross unrealized losses	1	0
Estimated fair value, fixed maturities	526	452
Indemnity | States & political subdivisions
Available-for-sale securities
Amortized cost, fixed maturities	237	172
Gross unrealized gains	7	13
Gross unrealized losses	1	0
Estimated fair value, fixed maturities	243	185
Indemnity | Corporate debt securities
Available-for-sale securities
Amortized cost, fixed maturities	280	259
Gross unrealized gains	2	2
Gross unrealized losses	0	0
Estimated fair value, fixed maturities	282	261
Indemnity | Commercial mortgage-backed securities
Available-for-sale securities
Amortized cost, fixed maturities		3
Gross unrealized gains		0
Gross unrealized losses		0
Estimated fair value, fixed maturities		3
Indemnity | Collateralized debt obligations
Available-for-sale securities
Amortized cost, fixed maturities	1	3
Gross unrealized gains	0	0
Gross unrealized losses	0	0
Estimated fair value, fixed maturities	1	3
Indemnity | Nonredeemable preferred stock
Available-for-sale securities
Amortized cost, equity securities	24	28
Gross unrealized gains	2	2
Gross unrealized losses	1	1
Estimated fair value, equity securities	25	29
Indemnity | Common stock
Available-for-sale securities
Amortized cost, equity securities	26	26
Gross unrealized gains	0	0
Gross unrealized losses	1	0
Estimated fair value, equity securities	25	26
Exchange
Available-for-sale securities
Amortized cost, fixed maturities	7,801	7,016
Amortized cost, equity securities	778	871
Amortized cost	8,579	7,887
Gross unrealized gains	481	773
Gross unrealized losses	79	8
Estimated fair value, fixed maturities	8,162	7,707
Estimated fair value, equity securities	819	945
Estimated fair value	8,981	8,652
Exchange | Fixed maturities
Available-for-sale securities
Amortized cost, fixed maturities	7,801	7,016
Gross unrealized gains	426	696
Gross unrealized losses	65	5
Estimated fair value, fixed maturities	8,162	7,707
Exchange | U.S. government & agencies
Available-for-sale securities
Amortized cost, fixed maturities	171	190
Gross unrealized gains	1	2
Gross unrealized losses	0	1
Estimated fair value, fixed maturities	172	191
Exchange | States & political subdivisions
Available-for-sale securities
Amortized cost, fixed maturities	1,430	1,218
Gross unrealized gains	55	103
Gross unrealized losses	15	0
Estimated fair value, fixed maturities	1,470	1,321
Exchange | Foreign government securities
Available-for-sale securities
Amortized cost, fixed maturities	15	15
Gross unrealized gains	0	1
Gross unrealized losses	0	0
Estimated fair value, fixed maturities	15	16
Exchange | Corporate debt securities
Available-for-sale securities
Amortized cost, fixed maturities	5,902	5,211
Gross unrealized gains	354	569
Gross unrealized losses	45	3
Estimated fair value, fixed maturities	6,211	5,777
Exchange | Residential mortgage-backed securities
Available-for-sale securities
Amortized cost, fixed maturities	157	226
Gross unrealized gains	3	6
Gross unrealized losses	4	1
Estimated fair value, fixed maturities	156	231
Exchange | Commercial mortgage-backed securities
Available-for-sale securities
Amortized cost, fixed maturities	45	62
Gross unrealized gains	2	5
Gross unrealized losses	0	0
Estimated fair value, fixed maturities	47	67
Exchange | Collateralized debt obligations
Available-for-sale securities
Amortized cost, fixed maturities	8	43
Gross unrealized gains	8	6
Gross unrealized losses	0	0
Estimated fair value, fixed maturities	16	49
Exchange | Other debt securities
Available-for-sale securities
Amortized cost, fixed maturities	73	51
Gross unrealized gains	3	4
Gross unrealized losses	1	0
Estimated fair value, fixed maturities	75	55
Exchange | Nonredeemable preferred stock
Available-for-sale securities
Amortized cost, equity securities	577	555
Gross unrealized gains	55	77
Gross unrealized losses	11	1
Estimated fair value, equity securities	621	631
Exchange | Common stock
Available-for-sale securities
Amortized cost, equity securities	201	316
Gross unrealized gains	0	0
Gross unrealized losses	3	2
Estimated fair value, equity securities	$ 198	$ 314