Fair Value Measurements Fair Value Measurement (Details) (USD $)	Sep. 30, 2012	Dec. 31, 2011	Jun. 30, 2012 Fixed maturities	Dec. 31, 2011 Fixed maturities	Jun. 30, 2012 U.S. Treasuries	Dec. 31, 2011 U.S. Treasuries	Jun. 30, 2012 U.S government agencies and authorities	Dec. 31, 2011 U.S government agencies and authorities	Jun. 30, 2012 Foreign		Dec. 31, 2011 Foreign		Jun. 30, 2012 Residential mortgage-backed securities	Dec. 31, 2011 Residential mortgage-backed securities	Jun. 30, 2012 Commercial mortgage-backed securities	Dec. 31, 2011 Commercial mortgage-backed securities	Sep. 30, 2012 Measured at fair value on a recurring basis Level 1	Dec. 31, 2011 Measured at fair value on a recurring basis Level 1	Sep. 30, 2012 Measured at fair value on a recurring basis Level 1 Fixed Indexed Annuities (FIA)	Dec. 31, 2011 Measured at fair value on a recurring basis Level 1 Fixed Indexed Annuities (FIA)	Sep. 30, 2012 Measured at fair value on a recurring basis Level 1 GMAB / GMWB / GMWBL		Dec. 31, 2011 Measured at fair value on a recurring basis Level 1 GMAB / GMWB / GMWBL	Sep. 30, 2012 Measured at fair value on a recurring basis Level 1 Embedded derivative on reinsurance	Dec. 31, 2011 Measured at fair value on a recurring basis Level 1 Embedded derivative on reinsurance	Sep. 30, 2012 Measured at fair value on a recurring basis Level 1 Interest rate contracts	Dec. 31, 2011 Measured at fair value on a recurring basis Level 1 Interest rate contracts	Sep. 30, 2012 Measured at fair value on a recurring basis Level 1 Foreign exchange contracts	Dec. 31, 2011 Measured at fair value on a recurring basis Level 1 Foreign exchange contracts	Sep. 30, 2012 Measured at fair value on a recurring basis Level 1 Equity contracts	Dec. 31, 2011 Measured at fair value on a recurring basis Level 1 Equity contracts	Sep. 30, 2012 Measured at fair value on a recurring basis Level 1 Credit contracts	Dec. 31, 2011 Measured at fair value on a recurring basis Level 1 Credit contracts	Sep. 30, 2012 Measured at fair value on a recurring basis Level 1 U.S. Treasuries	Dec. 31, 2011 Measured at fair value on a recurring basis Level 1 U.S. Treasuries	Sep. 30, 2012 Measured at fair value on a recurring basis Level 1 U.S government agencies and authorities	Dec. 31, 2011 Measured at fair value on a recurring basis Level 1 U.S government agencies and authorities	Sep. 30, 2012 Measured at fair value on a recurring basis Level 1 U.S. corporate, state and municipalities	Dec. 31, 2011 Measured at fair value on a recurring basis Level 1 U.S. corporate, state and municipalities	Sep. 30, 2012 Measured at fair value on a recurring basis Level 1 Foreign	Dec. 31, 2011 Measured at fair value on a recurring basis Level 1 Foreign	Sep. 30, 2012 Measured at fair value on a recurring basis Level 1 Residential mortgage-backed securities	Dec. 31, 2011 Measured at fair value on a recurring basis Level 1 Residential mortgage-backed securities	Sep. 30, 2012 Measured at fair value on a recurring basis Level 1 Commercial mortgage-backed securities	Dec. 31, 2011 Measured at fair value on a recurring basis Level 1 Commercial mortgage-backed securities	Sep. 30, 2012 Measured at fair value on a recurring basis Level 1 Other asset-backed securities	Dec. 31, 2011 Measured at fair value on a recurring basis Level 1 Other asset-backed securities	Sep. 30, 2012 Measured at fair value on a recurring basis Level 1 Equity securities, available-for-sale	Dec. 31, 2011 Measured at fair value on a recurring basis Level 1 Equity securities, available-for-sale	Sep. 30, 2012 Measured at fair value on a recurring basis Level 2	Dec. 31, 2011 Measured at fair value on a recurring basis Level 2	Sep. 30, 2012 Measured at fair value on a recurring basis Level 2 Fixed Indexed Annuities (FIA)	Dec. 31, 2011 Measured at fair value on a recurring basis Level 2 Fixed Indexed Annuities (FIA)	Sep. 30, 2012 Measured at fair value on a recurring basis Level 2 GMAB / GMWB / GMWBL		Dec. 31, 2011 Measured at fair value on a recurring basis Level 2 GMAB / GMWB / GMWBL	Sep. 30, 2012 Measured at fair value on a recurring basis Level 2 Embedded derivative on reinsurance	Dec. 31, 2011 Measured at fair value on a recurring basis Level 2 Embedded derivative on reinsurance	Sep. 30, 2012 Measured at fair value on a recurring basis Level 2 Interest rate contracts	Dec. 31, 2011 Measured at fair value on a recurring basis Level 2 Interest rate contracts	Sep. 30, 2012 Measured at fair value on a recurring basis Level 2 Foreign exchange contracts	Dec. 31, 2011 Measured at fair value on a recurring basis Level 2 Foreign exchange contracts	Sep. 30, 2012 Measured at fair value on a recurring basis Level 2 Equity contracts	Dec. 31, 2011 Measured at fair value on a recurring basis Level 2 Equity contracts	Sep. 30, 2012 Measured at fair value on a recurring basis Level 2 Credit contracts	Dec. 31, 2011 Measured at fair value on a recurring basis Level 2 Credit contracts	Sep. 30, 2012 Measured at fair value on a recurring basis Level 2 U.S. Treasuries	Dec. 31, 2011 Measured at fair value on a recurring basis Level 2 U.S. Treasuries	Sep. 30, 2012 Measured at fair value on a recurring basis Level 2 U.S government agencies and authorities	Dec. 31, 2011 Measured at fair value on a recurring basis Level 2 U.S government agencies and authorities	Sep. 30, 2012 Measured at fair value on a recurring basis Level 2 U.S. corporate, state and municipalities	Dec. 31, 2011 Measured at fair value on a recurring basis Level 2 U.S. corporate, state and municipalities	Sep. 30, 2012 Measured at fair value on a recurring basis Level 2 Foreign	Dec. 31, 2011 Measured at fair value on a recurring basis Level 2 Foreign	Sep. 30, 2012 Measured at fair value on a recurring basis Level 2 Residential mortgage-backed securities	Dec. 31, 2011 Measured at fair value on a recurring basis Level 2 Residential mortgage-backed securities	Sep. 30, 2012 Measured at fair value on a recurring basis Level 2 Commercial mortgage-backed securities	Dec. 31, 2011 Measured at fair value on a recurring basis Level 2 Commercial mortgage-backed securities	Sep. 30, 2012 Measured at fair value on a recurring basis Level 2 Other asset-backed securities	Dec. 31, 2011 Measured at fair value on a recurring basis Level 2 Other asset-backed securities	Sep. 30, 2012 Measured at fair value on a recurring basis Level 2 Equity securities, available-for-sale	Dec. 31, 2011 Measured at fair value on a recurring basis Level 2 Equity securities, available-for-sale	Sep. 30, 2012 Measured at fair value on a recurring basis Level 3	Dec. 31, 2011 Measured at fair value on a recurring basis Level 3	Sep. 30, 2012 Measured at fair value on a recurring basis Level 3 Fixed Indexed Annuities (FIA)	Dec. 31, 2011 Measured at fair value on a recurring basis Level 3 Fixed Indexed Annuities (FIA)	Sep. 30, 2012 Measured at fair value on a recurring basis Level 3 GMAB / GMWB / GMWBL		Dec. 31, 2011 Measured at fair value on a recurring basis Level 3 GMAB / GMWB / GMWBL	Sep. 30, 2012 Measured at fair value on a recurring basis Level 3 Embedded derivative on reinsurance	Dec. 31, 2011 Measured at fair value on a recurring basis Level 3 Embedded derivative on reinsurance	Sep. 30, 2012 Measured at fair value on a recurring basis Level 3 Interest rate contracts	Dec. 31, 2011 Measured at fair value on a recurring basis Level 3 Interest rate contracts	Sep. 30, 2012 Measured at fair value on a recurring basis Level 3 Foreign exchange contracts	Dec. 31, 2011 Measured at fair value on a recurring basis Level 3 Foreign exchange contracts	Sep. 30, 2012 Measured at fair value on a recurring basis Level 3 Equity contracts	Dec. 31, 2011 Measured at fair value on a recurring basis Level 3 Equity contracts	Sep. 30, 2012 Measured at fair value on a recurring basis Level 3 Credit contracts	Dec. 31, 2011 Measured at fair value on a recurring basis Level 3 Credit contracts	Sep. 30, 2012 Measured at fair value on a recurring basis Level 3 U.S. Treasuries	Dec. 31, 2011 Measured at fair value on a recurring basis Level 3 U.S. Treasuries	Sep. 30, 2012 Measured at fair value on a recurring basis Level 3 U.S government agencies and authorities	Dec. 31, 2011 Measured at fair value on a recurring basis Level 3 U.S government agencies and authorities	Sep. 30, 2012 Measured at fair value on a recurring basis Level 3 U.S. corporate, state and municipalities	Dec. 31, 2011 Measured at fair value on a recurring basis Level 3 U.S. corporate, state and municipalities	Sep. 30, 2012 Measured at fair value on a recurring basis Level 3 Foreign	Dec. 31, 2011 Measured at fair value on a recurring basis Level 3 Foreign	Sep. 30, 2012 Measured at fair value on a recurring basis Level 3 Residential mortgage-backed securities	Dec. 31, 2011 Measured at fair value on a recurring basis Level 3 Residential mortgage-backed securities	Sep. 30, 2012 Measured at fair value on a recurring basis Level 3 Commercial mortgage-backed securities	Dec. 31, 2011 Measured at fair value on a recurring basis Level 3 Commercial mortgage-backed securities	Sep. 30, 2012 Measured at fair value on a recurring basis Level 3 Other asset-backed securities	Dec. 31, 2011 Measured at fair value on a recurring basis Level 3 Other asset-backed securities	Sep. 30, 2012 Measured at fair value on a recurring basis Level 3 Equity securities, available-for-sale	Dec. 31, 2011 Measured at fair value on a recurring basis Level 3 Equity securities, available-for-sale	Sep. 30, 2012 Measured at fair value on a recurring basis Total	Dec. 31, 2011 Measured at fair value on a recurring basis Total	Sep. 30, 2012 Measured at fair value on a recurring basis Total Fixed Indexed Annuities (FIA)	Dec. 31, 2011 Measured at fair value on a recurring basis Total Fixed Indexed Annuities (FIA)	Sep. 30, 2012 Measured at fair value on a recurring basis Total GMAB / GMWB / GMWBL		Dec. 31, 2011 Measured at fair value on a recurring basis Total GMAB / GMWB / GMWBL	Sep. 30, 2012 Measured at fair value on a recurring basis Total Embedded derivative on reinsurance	Dec. 31, 2011 Measured at fair value on a recurring basis Total Embedded derivative on reinsurance	Sep. 30, 2012 Measured at fair value on a recurring basis Total Interest rate contracts	Dec. 31, 2011 Measured at fair value on a recurring basis Total Interest rate contracts	Sep. 30, 2012 Measured at fair value on a recurring basis Total Foreign exchange contracts	Dec. 31, 2011 Measured at fair value on a recurring basis Total Foreign exchange contracts	Sep. 30, 2012 Measured at fair value on a recurring basis Total Equity contracts	Dec. 31, 2011 Measured at fair value on a recurring basis Total Equity contracts	Sep. 30, 2012 Measured at fair value on a recurring basis Total Credit contracts	Dec. 31, 2011 Measured at fair value on a recurring basis Total Credit contracts	Sep. 30, 2012 Measured at fair value on a recurring basis Total U.S. Treasuries	Dec. 31, 2011 Measured at fair value on a recurring basis Total U.S. Treasuries	Sep. 30, 2012 Measured at fair value on a recurring basis Total U.S government agencies and authorities	Dec. 31, 2011 Measured at fair value on a recurring basis Total U.S government agencies and authorities	Sep. 30, 2012 Measured at fair value on a recurring basis Total U.S. corporate, state and municipalities	Dec. 31, 2011 Measured at fair value on a recurring basis Total U.S. corporate, state and municipalities	Sep. 30, 2012 Measured at fair value on a recurring basis Total Foreign	Dec. 31, 2011 Measured at fair value on a recurring basis Total Foreign	Sep. 30, 2012 Measured at fair value on a recurring basis Total Residential mortgage-backed securities	Dec. 31, 2011 Measured at fair value on a recurring basis Total Residential mortgage-backed securities	Sep. 30, 2012 Measured at fair value on a recurring basis Total Commercial mortgage-backed securities	Dec. 31, 2011 Measured at fair value on a recurring basis Total Commercial mortgage-backed securities	Sep. 30, 2012 Measured at fair value on a recurring basis Total Other asset-backed securities	Dec. 31, 2011 Measured at fair value on a recurring basis Total Other asset-backed securities	Sep. 30, 2012 Measured at fair value on a recurring basis Total Equity securities, available-for-sale	Dec. 31, 2011 Measured at fair value on a recurring basis Total Equity securities, available-for-sale
Assets Measured on Recurring Basis [Abstract]
Fixed maturities, including securities pledged, Fair Value			$ 21,968,300,000	$ 22,748,500,000	$ 1,368,800,000	$ 1,785,800,000	$ 23,800,000	$ 23,700,000	$ 450,000,000	[1]	$ 370,300,000	[1]	$ 1,998,600,000	$ 2,305,800,000	$ 1,826,400,000	$ 2,001,900,000	$ 1,360,900,000	$ 1,778,000,000																$ 1,360,900,000	$ 1,778,000,000	$ 0	$ 0	$ 0	$ 0	$ 0	$ 0	$ 0	$ 0	$ 0	$ 0	$ 0	$ 0			$ 20,344,500,000	$ 20,655,600,000																$ 7,900,000	$ 7,800,000	$ 23,800,000	$ 23,700,000	$ 10,581,100,000	$ 10,251,100,000	$ 5,325,400,000	$ 5,525,200,000	$ 1,974,700,000	$ 2,245,100,000	$ 1,826,400,000	$ 2,001,900,000	$ 605,200,000	$ 600,800,000			$ 262,900,000	$ 314,900,000																$ 0	$ 0	$ 0	$ 0	$ 132,100,000	$ 124,500,000	$ 22,300,000	$ 56,900,000	$ 23,900,000	$ 60,700,000	$ 0	$ 0	$ 84,600,000	$ 72,800,000			$ 21,968,300,000	$ 22,748,500,000																$ 1,368,800,000	$ 1,785,800,000	$ 23,800,000	$ 23,700,000	$ 10,713,200,000	$ 10,375,600,000	$ 5,347,700,000	$ 5,582,100,000	$ 1,998,600,000	$ 2,305,800,000	$ 1,826,400,000	$ 2,001,900,000	$ 689,800,000	$ 673,600,000
Available-for-sale Securities, Equity Securities	29,800,000	27,700,000																																														13,800,000	11,400,000																																0	0																																16,000,000	16,300,000																																29,800,000	27,700,000
Derivatives	1,628,800,000	1,609,100,000																								6,600,000	4,000,000	0	0	60,500,000	26,500,000	0	0																										1,459,100,000	1,534,400,000	15,000,000	9,700,000	56,300,000	0	500,000	900,000																										0	0	0	0	30,800,000	33,600,000		0																										1,465,700,000	1,538,400,000	15,000,000	9,700,000	147,600,000	60,100,000	500,000	900,000
Cash and cash equivalents, short-term investments and short-term investments under securities loan agreement																	2,247,500,000	2,760,700,000																																0	5,800,000																																0	0																																2,247,500,000	2,766,500,000
Assets held in separate accounts																	40,435,900,000	39,356,900,000																																0	0																																0	0																																40,435,900,000	39,356,900,000
Total																	44,125,200,000	43,937,500,000																																21,875,400,000	22,206,400,000																																309,700,000	364,800,000																																66,310,300,000	66,508,700,000
Liabilities Measured on Recurring Basis [Abstract]
Investment contract guarantees																			0	0	0	[2]	0	0	0																											0	0	0	[2]	0	317,700,000	230,900,000																											1,403,600,000	1,282,200,000	1,946,100,000	[2]	2,229,900,000	0	0																											1,403,600,000	1,282,200,000	1,946,100,000	[2]	2,229,900,000	317,700,000	230,900,000
Derivatives																										0	0	0	0	3,200,000	3,300,000	0	0																										572,600,000	520,000,000	39,700,000	42,400,000	26,300,000	0	100,000	1,200,000																										0	0	0	0	0	25,100,000	0	12,900,000																										572,600,000	520,000,000	39,700,000	42,400,000	29,500,000	28,400,000	100,000	14,100,000
Total																	3,200,000	3,300,000																																956,400,000	794,500,000																																3,349,700,000	3,550,100,000																																4,309,300,000	4,347,900,000
Fixed maturities valued using unadjusted broker quotes	99,300,000
Fixed maturities valued using unadjusted prices	$ 16,800,000,000

[1] Primarily U.S. dollar denominated.

[2] Guaranteed minimum accumulation benefits ("GMAB"), Guaranteed minimum withdrawal benefits ("GMWB"), Guaranteed minimum withdrawal benefits with life payouts ("GMWBL").