Investments (Details) (USD $) In Millions, unless otherwise specified	Jun. 30, 2014	Dec. 31, 2013
Available-for-sale securities
Amortized cost	$ 9,500	$ 9,147
Gross unrealized gains	654	492
Gross unrealized losses	16	82
Estimated fair value, fixed maturities	9,198	8,688
Estimated fair value, equity securities	940	869
Estimated fair value	10,138	9,557
Indemnity
Available-for-sale securities
Amortized cost, fixed maturities	484	518
Amortized cost, equity securities	25	50
Amortized cost	509	568
Gross unrealized gains	15	11
Gross unrealized losses	1	3
Estimated fair value, fixed maturities	497	526
Estimated fair value, equity securities	26	50
Estimated fair value	523	576
Indemnity | Fixed maturities
Available-for-sale securities
Amortized cost, fixed maturities	484	518
Gross unrealized gains	13	9
Gross unrealized losses	0	1
Estimated fair value, fixed maturities	497	526
Indemnity | States & political subdivisions
Available-for-sale securities
Amortized cost, fixed maturities	230	237
Gross unrealized gains	11	7
Gross unrealized losses	0	1
Estimated fair value, fixed maturities	241	243
Indemnity | Corporate debt securities
Available-for-sale securities
Amortized cost, fixed maturities	254	280
Gross unrealized gains	2	2
Gross unrealized losses	0	0
Estimated fair value, fixed maturities	256	282
Indemnity | Collateralized debt obligations
Available-for-sale securities
Amortized cost, fixed maturities	0	1
Gross unrealized gains	0	0
Gross unrealized losses	0	0
Estimated fair value, fixed maturities	0	1
Indemnity | Nonredeemable preferred stock
Available-for-sale securities
Amortized cost, equity securities	12	24
Gross unrealized gains	2	2
Gross unrealized losses	0	1
Estimated fair value, equity securities	14	25
Indemnity | Common stock
Available-for-sale securities
Amortized cost, equity securities	13	26
Gross unrealized gains	0	0
Gross unrealized losses	1	1
Estimated fair value, equity securities	12	25
Exchange
Available-for-sale securities
Amortized cost, fixed maturities	8,149	7,801
Amortized cost, equity securities	842	778
Amortized cost	8,991	8,579
Gross unrealized gains	639	481
Gross unrealized losses	15	79
Estimated fair value, fixed maturities	8,701	8,162
Estimated fair value, equity securities	914	819
Estimated fair value	9,615	8,981
Exchange | Fixed maturities
Available-for-sale securities
Amortized cost, fixed maturities	8,149	7,801
Gross unrealized gains	564	426
Gross unrealized losses	12	65
Estimated fair value, fixed maturities	8,701	8,162
Exchange | U.S. government & agencies
Available-for-sale securities
Amortized cost, fixed maturities		171
Gross unrealized gains		1
Gross unrealized losses		0
Estimated fair value, fixed maturities		172
Exchange | U.S. treasury
Available-for-sale securities
Amortized cost, fixed maturities	31
Gross unrealized gains	0
Gross unrealized losses	0
Estimated fair value, fixed maturities	31
Exchange | Government sponsored enterprises
Available-for-sale securities
Amortized cost, fixed maturities	3
Gross unrealized gains	1
Gross unrealized losses	0
Estimated fair value, fixed maturities	4
Exchange | States & political subdivisions
Available-for-sale securities
Amortized cost, fixed maturities	1,438	1,430
Gross unrealized gains	83	55
Gross unrealized losses	2	15
Estimated fair value, fixed maturities	1,519	1,470
Exchange | Foreign government securities
Available-for-sale securities
Amortized cost, fixed maturities	15	15
Gross unrealized gains	0	0
Gross unrealized losses	0	0
Estimated fair value, fixed maturities	15	15
Exchange | Corporate debt securities
Available-for-sale securities
Amortized cost, fixed maturities	6,409	5,902
Gross unrealized gains	465	354
Gross unrealized losses	8	45
Estimated fair value, fixed maturities	6,866	6,211
Exchange | Residential mortgage-backed securities
Available-for-sale securities
Amortized cost, fixed maturities	145	157
Gross unrealized gains	3	3
Gross unrealized losses	2	4
Estimated fair value, fixed maturities	146	156
Exchange | Commercial mortgage-backed securities
Available-for-sale securities
Amortized cost, fixed maturities	32	45
Gross unrealized gains	2	2
Gross unrealized losses	0	0
Estimated fair value, fixed maturities	34	47
Exchange | Collateralized debt obligations
Available-for-sale securities
Amortized cost, fixed maturities	7	8
Gross unrealized gains	7	8
Gross unrealized losses	0	0
Estimated fair value, fixed maturities	14	16
Exchange | Other debt securities
Available-for-sale securities
Amortized cost, fixed maturities	69	73
Gross unrealized gains	3	3
Gross unrealized losses	0	1
Estimated fair value, fixed maturities	72	75
Exchange | Nonredeemable preferred stock
Available-for-sale securities
Amortized cost, equity securities	646	577
Gross unrealized gains	73	55
Gross unrealized losses	2	11
Estimated fair value, equity securities	717	621
Exchange | Common stock
Available-for-sale securities
Amortized cost, equity securities	196	201
Gross unrealized gains	2	0
Gross unrealized losses	1	3
Estimated fair value, equity securities	$ 197	$ 198