Fair Value (Details) (USD $) In Millions, unless otherwise specified	9 Months Ended																																																																																									9 Months Ended	12 Months Ended																																																																																																													9 Months Ended	12 Months Ended	9 Months Ended	12 Months Ended	9 Months Ended	12 Months Ended
	Sep. 30, 2014	Sep. 30, 2013	Dec. 31, 2013	Sep. 30, 2014 Fair value measurements on a recurring basis	Dec. 31, 2013 Fair value measurements on a recurring basis	Sep. 30, 2014 Fair value measurements on a recurring basis Level 1	Dec. 31, 2013 Fair value measurements on a recurring basis Level 1	Sep. 30, 2014 Fair value measurements on a recurring basis Level 2	Dec. 31, 2013 Fair value measurements on a recurring basis Level 2	Sep. 30, 2014 Fair value measurements on a recurring basis Level 3	Dec. 31, 2013 Fair value measurements on a recurring basis Level 3	Sep. 30, 2014 Fair value measurements on a recurring basis Level 3 Real estate fund	Dec. 31, 2013 Fair value measurements on a recurring basis Level 3 Real estate fund	Sep. 30, 2014 Indemnity	Dec. 31, 2013 Indemnity	Sep. 30, 2014 Indemnity Fair value measurements on a recurring basis	Dec. 31, 2013 Indemnity Fair value measurements on a recurring basis	Sep. 30, 2014 Indemnity Fair value measurements on a recurring basis Fixed maturities	Dec. 31, 2013 Indemnity Fair value measurements on a recurring basis Fixed maturities	Sep. 30, 2014 Indemnity Fair value measurements on a recurring basis States & political subdivisions	Dec. 31, 2013 Indemnity Fair value measurements on a recurring basis States & political subdivisions	Sep. 30, 2014 Indemnity Fair value measurements on a recurring basis Corporate debt securities	Dec. 31, 2013 Indemnity Fair value measurements on a recurring basis Corporate debt securities	Sep. 30, 2014 Indemnity Fair value measurements on a recurring basis Residential mortgage-backed securities	Sep. 30, 2014 Indemnity Fair value measurements on a recurring basis Commercial mortgage-backed securities	Sep. 30, 2014 Indemnity Fair value measurements on a recurring basis Collateralized debt obligations	Dec. 31, 2013 Indemnity Fair value measurements on a recurring basis Collateralized debt obligations	Sep. 30, 2014 Indemnity Fair value measurements on a recurring basis Other debt securities	Sep. 30, 2014 Indemnity Fair value measurements on a recurring basis Nonredeemable preferred stock	Dec. 31, 2013 Indemnity Fair value measurements on a recurring basis Nonredeemable preferred stock	Sep. 30, 2014 Indemnity Fair value measurements on a recurring basis Common stock	Dec. 31, 2013 Indemnity Fair value measurements on a recurring basis Common stock	Sep. 30, 2014 Indemnity Fair value measurements on a recurring basis Real estate	Dec. 31, 2013 Indemnity Fair value measurements on a recurring basis Real estate	Sep. 30, 2014 Indemnity Fair value measurements on a recurring basis Level 1	Dec. 31, 2013 Indemnity Fair value measurements on a recurring basis Level 1	Sep. 30, 2014 Indemnity Fair value measurements on a recurring basis Level 1 Fixed maturities	Dec. 31, 2013 Indemnity Fair value measurements on a recurring basis Level 1 Fixed maturities	Sep. 30, 2014 Indemnity Fair value measurements on a recurring basis Level 1 States & political subdivisions	Dec. 31, 2013 Indemnity Fair value measurements on a recurring basis Level 1 States & political subdivisions	Sep. 30, 2014 Indemnity Fair value measurements on a recurring basis Level 1 Corporate debt securities	Dec. 31, 2013 Indemnity Fair value measurements on a recurring basis Level 1 Corporate debt securities	Sep. 30, 2014 Indemnity Fair value measurements on a recurring basis Level 1 Residential mortgage-backed securities	Sep. 30, 2014 Indemnity Fair value measurements on a recurring basis Level 1 Commercial mortgage-backed securities	Sep. 30, 2014 Indemnity Fair value measurements on a recurring basis Level 1 Collateralized debt obligations	Dec. 31, 2013 Indemnity Fair value measurements on a recurring basis Level 1 Collateralized debt obligations	Sep. 30, 2014 Indemnity Fair value measurements on a recurring basis Level 1 Other debt securities	Sep. 30, 2014 Indemnity Fair value measurements on a recurring basis Level 1 Nonredeemable preferred stock	Dec. 31, 2013 Indemnity Fair value measurements on a recurring basis Level 1 Nonredeemable preferred stock	Sep. 30, 2014 Indemnity Fair value measurements on a recurring basis Level 1 Common stock	Dec. 31, 2013 Indemnity Fair value measurements on a recurring basis Level 1 Common stock	Sep. 30, 2014 Indemnity Fair value measurements on a recurring basis Level 1 Real estate	Dec. 31, 2013 Indemnity Fair value measurements on a recurring basis Level 1 Real estate	Sep. 30, 2014 Indemnity Fair value measurements on a recurring basis Level 2	Dec. 31, 2013 Indemnity Fair value measurements on a recurring basis Level 2	Sep. 30, 2014 Indemnity Fair value measurements on a recurring basis Level 2 Fixed maturities	Dec. 31, 2013 Indemnity Fair value measurements on a recurring basis Level 2 Fixed maturities	Sep. 30, 2014 Indemnity Fair value measurements on a recurring basis Level 2 States & political subdivisions	Dec. 31, 2013 Indemnity Fair value measurements on a recurring basis Level 2 States & political subdivisions	Sep. 30, 2014 Indemnity Fair value measurements on a recurring basis Level 2 Corporate debt securities	Dec. 31, 2013 Indemnity Fair value measurements on a recurring basis Level 2 Corporate debt securities	Sep. 30, 2014 Indemnity Fair value measurements on a recurring basis Level 2 Residential mortgage-backed securities	Sep. 30, 2014 Indemnity Fair value measurements on a recurring basis Level 2 Commercial mortgage-backed securities	Sep. 30, 2014 Indemnity Fair value measurements on a recurring basis Level 2 Collateralized debt obligations	Dec. 31, 2013 Indemnity Fair value measurements on a recurring basis Level 2 Collateralized debt obligations	Sep. 30, 2014 Indemnity Fair value measurements on a recurring basis Level 2 Other debt securities	Sep. 30, 2014 Indemnity Fair value measurements on a recurring basis Level 2 Nonredeemable preferred stock	Dec. 31, 2013 Indemnity Fair value measurements on a recurring basis Level 2 Nonredeemable preferred stock	Sep. 30, 2014 Indemnity Fair value measurements on a recurring basis Level 2 Common stock	Dec. 31, 2013 Indemnity Fair value measurements on a recurring basis Level 2 Common stock	Sep. 30, 2014 Indemnity Fair value measurements on a recurring basis Level 2 Real estate	Dec. 31, 2013 Indemnity Fair value measurements on a recurring basis Level 2 Real estate	Sep. 30, 2014 Indemnity Fair value measurements on a recurring basis Level 3	Dec. 31, 2013 Indemnity Fair value measurements on a recurring basis Level 3	Sep. 30, 2014 Indemnity Fair value measurements on a recurring basis Level 3 Fixed maturities	Dec. 31, 2013 Indemnity Fair value measurements on a recurring basis Level 3 Fixed maturities	Sep. 30, 2014 Indemnity Fair value measurements on a recurring basis Level 3 States & political subdivisions	Dec. 31, 2013 Indemnity Fair value measurements on a recurring basis Level 3 States & political subdivisions	Sep. 30, 2014 Indemnity Fair value measurements on a recurring basis Level 3 Corporate debt securities	Dec. 31, 2013 Indemnity Fair value measurements on a recurring basis Level 3 Corporate debt securities	Sep. 30, 2014 Indemnity Fair value measurements on a recurring basis Level 3 Residential mortgage-backed securities	Sep. 30, 2014 Indemnity Fair value measurements on a recurring basis Level 3 Commercial mortgage-backed securities	Sep. 30, 2014 Indemnity Fair value measurements on a recurring basis Level 3 Collateralized debt obligations	Dec. 31, 2013 Indemnity Fair value measurements on a recurring basis Level 3 Collateralized debt obligations	Sep. 30, 2014 Indemnity Fair value measurements on a recurring basis Level 3 Other debt securities	Sep. 30, 2014 Indemnity Fair value measurements on a recurring basis Level 3 Nonredeemable preferred stock	Dec. 31, 2013 Indemnity Fair value measurements on a recurring basis Level 3 Nonredeemable preferred stock	Sep. 30, 2014 Indemnity Fair value measurements on a recurring basis Level 3 Common stock	Dec. 31, 2013 Indemnity Fair value measurements on a recurring basis Level 3 Common stock	Sep. 30, 2014 Indemnity Fair value measurements on a recurring basis Level 3 Real estate	Dec. 31, 2013 Indemnity Fair value measurements on a recurring basis Level 3 Real estate	Sep. 30, 2014 Exchange	Dec. 31, 2013 Exchange	Sep. 30, 2014 Exchange Fair value measurements on a recurring basis	Dec. 31, 2013 Exchange Fair value measurements on a recurring basis	Sep. 30, 2014 Exchange Fair value measurements on a recurring basis Fixed maturities	Dec. 31, 2013 Exchange Fair value measurements on a recurring basis Fixed maturities	Dec. 31, 2013 Exchange Fair value measurements on a recurring basis U.S. government & agencies	Sep. 30, 2014 Exchange Fair value measurements on a recurring basis U.S. treasury	Sep. 30, 2014 Exchange Fair value measurements on a recurring basis Government sponsored enterprises	Sep. 30, 2014 Exchange Fair value measurements on a recurring basis States & political subdivisions	Dec. 31, 2013 Exchange Fair value measurements on a recurring basis States & political subdivisions	Sep. 30, 2014 Exchange Fair value measurements on a recurring basis Foreign government securities	Dec. 31, 2013 Exchange Fair value measurements on a recurring basis Foreign government securities	Sep. 30, 2014 Exchange Fair value measurements on a recurring basis Corporate debt securities	Dec. 31, 2013 Exchange Fair value measurements on a recurring basis Corporate debt securities	Sep. 30, 2014 Exchange Fair value measurements on a recurring basis Residential mortgage-backed securities	Dec. 31, 2013 Exchange Fair value measurements on a recurring basis Residential mortgage-backed securities	Sep. 30, 2014 Exchange Fair value measurements on a recurring basis Commercial mortgage-backed securities	Dec. 31, 2013 Exchange Fair value measurements on a recurring basis Commercial mortgage-backed securities	Sep. 30, 2014 Exchange Fair value measurements on a recurring basis Collateralized debt obligations	Dec. 31, 2013 Exchange Fair value measurements on a recurring basis Collateralized debt obligations	Sep. 30, 2014 Exchange Fair value measurements on a recurring basis Other debt securities	Dec. 31, 2013 Exchange Fair value measurements on a recurring basis Other debt securities	Sep. 30, 2014 Exchange Fair value measurements on a recurring basis Nonredeemable preferred stock	Dec. 31, 2013 Exchange Fair value measurements on a recurring basis Nonredeemable preferred stock	Sep. 30, 2014 Exchange Fair value measurements on a recurring basis Common stock	Dec. 31, 2013 Exchange Fair value measurements on a recurring basis Common stock	Sep. 30, 2014 Exchange Fair value measurements on a recurring basis Real estate	Dec. 31, 2013 Exchange Fair value measurements on a recurring basis Real estate	Sep. 30, 2014 Exchange Fair value measurements on a recurring basis Level 1	Dec. 31, 2013 Exchange Fair value measurements on a recurring basis Level 1	Sep. 30, 2014 Exchange Fair value measurements on a recurring basis Level 1 Fixed maturities	Dec. 31, 2013 Exchange Fair value measurements on a recurring basis Level 1 Fixed maturities	Dec. 31, 2013 Exchange Fair value measurements on a recurring basis Level 1 U.S. government & agencies	Sep. 30, 2014 Exchange Fair value measurements on a recurring basis Level 1 U.S. treasury	Sep. 30, 2014 Exchange Fair value measurements on a recurring basis Level 1 Government sponsored enterprises	Sep. 30, 2014 Exchange Fair value measurements on a recurring basis Level 1 States & political subdivisions	Dec. 31, 2013 Exchange Fair value measurements on a recurring basis Level 1 States & political subdivisions	Sep. 30, 2014 Exchange Fair value measurements on a recurring basis Level 1 Foreign government securities	Dec. 31, 2013 Exchange Fair value measurements on a recurring basis Level 1 Foreign government securities	Sep. 30, 2014 Exchange Fair value measurements on a recurring basis Level 1 Corporate debt securities	Dec. 31, 2013 Exchange Fair value measurements on a recurring basis Level 1 Corporate debt securities	Sep. 30, 2014 Exchange Fair value measurements on a recurring basis Level 1 Residential mortgage-backed securities	Dec. 31, 2013 Exchange Fair value measurements on a recurring basis Level 1 Residential mortgage-backed securities	Sep. 30, 2014 Exchange Fair value measurements on a recurring basis Level 1 Commercial mortgage-backed securities	Dec. 31, 2013 Exchange Fair value measurements on a recurring basis Level 1 Commercial mortgage-backed securities	Sep. 30, 2014 Exchange Fair value measurements on a recurring basis Level 1 Collateralized debt obligations	Dec. 31, 2013 Exchange Fair value measurements on a recurring basis Level 1 Collateralized debt obligations	Sep. 30, 2014 Exchange Fair value measurements on a recurring basis Level 1 Other debt securities	Dec. 31, 2013 Exchange Fair value measurements on a recurring basis Level 1 Other debt securities	Sep. 30, 2014 Exchange Fair value measurements on a recurring basis Level 1 Nonredeemable preferred stock	Dec. 31, 2013 Exchange Fair value measurements on a recurring basis Level 1 Nonredeemable preferred stock	Sep. 30, 2014 Exchange Fair value measurements on a recurring basis Level 1 Common stock	Dec. 31, 2013 Exchange Fair value measurements on a recurring basis Level 1 Common stock	Sep. 30, 2014 Exchange Fair value measurements on a recurring basis Level 1 Real estate	Dec. 31, 2013 Exchange Fair value measurements on a recurring basis Level 1 Real estate	Sep. 30, 2014 Exchange Fair value measurements on a recurring basis Level 2	Dec. 31, 2013 Exchange Fair value measurements on a recurring basis Level 2	Sep. 30, 2014 Exchange Fair value measurements on a recurring basis Level 2 Fixed maturities	Dec. 31, 2013 Exchange Fair value measurements on a recurring basis Level 2 Fixed maturities	Dec. 31, 2013 Exchange Fair value measurements on a recurring basis Level 2 U.S. government & agencies	Sep. 30, 2014 Exchange Fair value measurements on a recurring basis Level 2 U.S. treasury	Sep. 30, 2014 Exchange Fair value measurements on a recurring basis Level 2 Government sponsored enterprises	Sep. 30, 2014 Exchange Fair value measurements on a recurring basis Level 2 States & political subdivisions	Dec. 31, 2013 Exchange Fair value measurements on a recurring basis Level 2 States & political subdivisions	Sep. 30, 2014 Exchange Fair value measurements on a recurring basis Level 2 Foreign government securities	Dec. 31, 2013 Exchange Fair value measurements on a recurring basis Level 2 Foreign government securities	Sep. 30, 2014 Exchange Fair value measurements on a recurring basis Level 2 Corporate debt securities	Dec. 31, 2013 Exchange Fair value measurements on a recurring basis Level 2 Corporate debt securities	Sep. 30, 2014 Exchange Fair value measurements on a recurring basis Level 2 Residential mortgage-backed securities	Dec. 31, 2013 Exchange Fair value measurements on a recurring basis Level 2 Residential mortgage-backed securities	Sep. 30, 2014 Exchange Fair value measurements on a recurring basis Level 2 Commercial mortgage-backed securities	Dec. 31, 2013 Exchange Fair value measurements on a recurring basis Level 2 Commercial mortgage-backed securities	Sep. 30, 2014 Exchange Fair value measurements on a recurring basis Level 2 Collateralized debt obligations	Dec. 31, 2013 Exchange Fair value measurements on a recurring basis Level 2 Collateralized debt obligations	Sep. 30, 2014 Exchange Fair value measurements on a recurring basis Level 2 Other debt securities	Dec. 31, 2013 Exchange Fair value measurements on a recurring basis Level 2 Other debt securities	Sep. 30, 2014 Exchange Fair value measurements on a recurring basis Level 2 Nonredeemable preferred stock	Dec. 31, 2013 Exchange Fair value measurements on a recurring basis Level 2 Nonredeemable preferred stock	Sep. 30, 2014 Exchange Fair value measurements on a recurring basis Level 2 Common stock	Dec. 31, 2013 Exchange Fair value measurements on a recurring basis Level 2 Common stock	Sep. 30, 2014 Exchange Fair value measurements on a recurring basis Level 2 Real estate	Dec. 31, 2013 Exchange Fair value measurements on a recurring basis Level 2 Real estate	Sep. 30, 2014 Exchange Fair value measurements on a recurring basis Level 3	Dec. 31, 2013 Exchange Fair value measurements on a recurring basis Level 3	Sep. 30, 2014 Exchange Fair value measurements on a recurring basis Level 3 Fixed maturities	Dec. 31, 2013 Exchange Fair value measurements on a recurring basis Level 3 Fixed maturities	Dec. 31, 2013 Exchange Fair value measurements on a recurring basis Level 3 U.S. government & agencies	Sep. 30, 2014 Exchange Fair value measurements on a recurring basis Level 3 U.S. treasury	Sep. 30, 2014 Exchange Fair value measurements on a recurring basis Level 3 Government sponsored enterprises	Sep. 30, 2014 Exchange Fair value measurements on a recurring basis Level 3 States & political subdivisions	Dec. 31, 2013 Exchange Fair value measurements on a recurring basis Level 3 States & political subdivisions	Sep. 30, 2014 Exchange Fair value measurements on a recurring basis Level 3 Foreign government securities	Dec. 31, 2013 Exchange Fair value measurements on a recurring basis Level 3 Foreign government securities	Sep. 30, 2014 Exchange Fair value measurements on a recurring basis Level 3 Corporate debt securities	Dec. 31, 2013 Exchange Fair value measurements on a recurring basis Level 3 Corporate debt securities	Sep. 30, 2014 Exchange Fair value measurements on a recurring basis Level 3 Residential mortgage-backed securities	Dec. 31, 2013 Exchange Fair value measurements on a recurring basis Level 3 Residential mortgage-backed securities	Sep. 30, 2014 Exchange Fair value measurements on a recurring basis Level 3 Commercial mortgage-backed securities	Dec. 31, 2013 Exchange Fair value measurements on a recurring basis Level 3 Commercial mortgage-backed securities	Sep. 30, 2014 Exchange Fair value measurements on a recurring basis Level 3 Collateralized debt obligations	Dec. 31, 2013 Exchange Fair value measurements on a recurring basis Level 3 Collateralized debt obligations	Sep. 30, 2014 Exchange Fair value measurements on a recurring basis Level 3 Other debt securities	Dec. 31, 2013 Exchange Fair value measurements on a recurring basis Level 3 Other debt securities	Sep. 30, 2014 Exchange Fair value measurements on a recurring basis Level 3 Nonredeemable preferred stock	Dec. 31, 2013 Exchange Fair value measurements on a recurring basis Level 3 Nonredeemable preferred stock	Sep. 30, 2014 Exchange Fair value measurements on a recurring basis Level 3 Common stock	Dec. 31, 2013 Exchange Fair value measurements on a recurring basis Level 3 Common stock	Sep. 30, 2014 Exchange Fair value measurements on a recurring basis Level 3 Real estate	Dec. 31, 2013 Exchange Fair value measurements on a recurring basis Level 3 Real estate	Sep. 30, 2014 Minimum Fair value measurements on a recurring basis Level 3 Real estate	Dec. 31, 2013 Minimum Fair value measurements on a recurring basis Level 3 Real estate	Sep. 30, 2014 Maximum Fair value measurements on a recurring basis Level 3 Real estate	Dec. 31, 2013 Maximum Fair value measurements on a recurring basis Level 3 Real estate
Fair value measurements on a recurring basis by asset class and level of input
Available-for-sale securities	$ 10,407		$ 9,557											$ 588	$ 576	$ 588	$ 576	$ 563	$ 526	$ 231	$ 243	$ 242	$ 282	$ 10	$ 49	$ 24	$ 1	$ 7	$ 12	$ 25	$ 13	$ 25			$ 15	$ 27	$ 0	$ 0	$ 0	$ 0	$ 0	$ 0	$ 0	$ 0	$ 0	$ 0	$ 0	$ 2	$ 2	$ 13	$ 25			$ 569	$ 547	$ 559	$ 524	$ 231	$ 243	$ 241	$ 281	$ 10	$ 46	$ 24	$ 0	$ 7	$ 10	$ 23	$ 0	$ 0			$ 4	$ 2	$ 4	$ 2	$ 0	$ 0	$ 1	$ 1	$ 0	$ 3	$ 0	$ 1	$ 0	$ 0	$ 0	$ 0	$ 0			$ 9,819	$ 8,981	$ 9,819	$ 8,981	$ 8,902	$ 8,162	$ 172	$ 6	$ 4	$ 1,483	$ 1,470	$ 15	$ 15	$ 7,161	$ 6,211	$ 119	$ 156	$ 33	$ 47	$ 11	$ 16	$ 70	$ 75	$ 720	$ 621	$ 197	$ 198			$ 531	$ 440	$ 0	$ 0	$ 0	$ 0	$ 0	$ 0	$ 0	$ 0	$ 0	$ 0	$ 0	$ 0	$ 0	$ 0	$ 0	$ 0	$ 0	$ 0	$ 0	$ 334	$ 242	$ 197	$ 198			$ 9,207	$ 8,510	$ 8,829	$ 8,131	$ 172	$ 6	$ 4	$ 1,483	$ 1,470	$ 15	$ 15	$ 7,090	$ 6,185	$ 119	$ 156	$ 33	$ 47	$ 11	$ 11	$ 68	$ 75	$ 378	$ 379	$ 0	$ 0			$ 81	$ 31	$ 73	$ 31	$ 0	$ 0	$ 0	$ 0	$ 0	$ 0	$ 0	$ 71	$ 26	$ 0	$ 0	$ 0	$ 0	$ 0	$ 5	$ 2	$ 0	$ 8	$ 0	$ 0	$ 0
Trading securities																																																																																														3,125	3,202																						3,125	3,202			3,110	3,187																						3,110	3,187			0	0																						0	0			15	15																						15	15
Other investments																																	19	18																		0	0																		0	0																		19	18																												103	98																										0	0																										0	0																										103	98
Total				13,654	12,875	3,656	3,654	9,776	9,057	222	164					607	594																		15	27																		569	547																		23	20																				13,047	12,281																										3,641	3,627																										9,207	8,510																										199	144
Other investments:
Number of real estate funds reported under fair value option												4	4
Underlying assets, liquidation period from inception of fund																																																																																																																																																																																																										5 years	5 years	10 years	10 years
Contributions made to the funds	82.0	66.0																																																																																								0	0																																																																																																													0	0
Distributions received from the funds	100.0	125.0																																																																																								2.6	2.4																																																																																																													9.7	21.7
Unfunded commitments																																																																																										$ 0.9	$ 1.5																																																																																																													$ 2.8	$ 4.5