Business, Basis of Presentation and Significant Accounting Polices (Details) (USD $) In Millions, unless otherwise specified	3 Months Ended		9 Months Ended		3 Months Ended		9 Months Ended		3 Months Ended	9 Months Ended	3 Months Ended		9 Months Ended		3 Months Ended		9 Months Ended
	Sep. 30, 2012	Sep. 30, 2011	Sep. 30, 2012	Sep. 30, 2011	Sep. 30, 2012 Before Change in Method	Sep. 30, 2011 Before Change in Method	Sep. 30, 2012 Before Change in Method	Sep. 30, 2011 Before Change in Method	Sep. 30, 2011 Effect of Changes	Sep. 30, 2011 Effect of Changes	Sep. 30, 2012 Effect of GMWBL Change Effect of Changes	Sep. 30, 2011 Effect of GMWBL Change Effect of Changes	Sep. 30, 2012 Effect of GMWBL Change Effect of Changes	Sep. 30, 2011 Effect of GMWBL Change Effect of Changes	Sep. 30, 2012 Effect of Pension Change Effect of Changes	Sep. 30, 2011 Effect of Pension Change Effect of Changes	Sep. 30, 2012 Effect of Pension Change Effect of Changes	Sep. 30, 2011 Effect of Pension Change Effect of Changes	Jan. 02, 2012 Retained Earnings (Deficit) Effect of GMWBL Change	Jan. 02, 2012 Retained Earnings (Deficit) Effect of Pension Change	Jan. 02, 2012 Accumulated Other Comprehensive Income (Loss) Effect of GMWBL Change	Jan. 02, 2012 Accumulated Other Comprehensive Income (Loss) Effect of Pension Change	Sep. 30, 2012 Accounting Standards Update 2010-26	Sep. 30, 2012 Accounting Standards Update 2010-26 Retained Earnings (Deficit)	Sep. 30, 2012 Accounting Standards Update 2010-26 Accumulated Other Comprehensive Income (Loss)
Retained Earnings Adjustments [Line Items]
Fee income	$ 196.8	$ 210.1	$ 609.8	$ 658.5		$ 261.4		$ 820.4	$ (51.3)	$ (161.9)		$ 0		$ 0		$ 0		$ 0
Other net realized capital gains (losses)	(208.9)	1,151.3	(1,061.0)	851.9	(694.3)	2,012.7	(1,332.0)	1,828.9	(861.4)	(977.0)	485.4	0	271.0	0	0	0	0	0
Other income	7.3	12.8	27.6	46.4		0.4		0.8	12.4	45.6		0		0		0		0
Interest credited and other benefits to contract owners	(173.5)	2,340.0	304.8	2,890.1		2,437.8		3,167.7	(900.4)	(1,100.0)		802.6		815.9		0		0
Effects of changes in accounting principle																			(15.9)	3.7	(22.3)	3.7		394.3	41.1
Taxes related to the effect of changes in accounting principle																							$ 212.3