Fair Value Measurements (Details 7) (USD $) In Millions, unless otherwise specified	Sep. 30, 2013	Dec. 31, 2012
Assets (liabilities)
Mortgage loans	$ 11,868.1	$ 11,519.7
Policy loans	859.6	864.9
Short-term debt	(175.5)	(40.8)
Long-term debt	(2,593.3)	(2,671.3)
Fair value hierarchy Level 1
Assets (liabilities)
Cash and cash equivalents not required to be reported at fair value	1,117.1	2,364.6
Bank deposits	(1,184.0)	(1,404.4)
Cash collateral payable	(30.0)	(205.6)
Fair value hierarchy Level 2
Assets (liabilities)
Other investments	136.3	195.3
Cash and cash equivalents not required to be reported at fair value		40.0
Investment-type insurance contracts	(6,396.7)	(7,367.4)
Short-term debt	(175.5)	(40.8)
Long-term debt	(2,677.0)	(2,921.7)
Bank deposits	(717.7)	(773.3)
Fair value hierarchy Level 3
Assets (liabilities)
Mortgage loans	12,190.9	12,163.7
Policy loans	988.6	1,056.8
Other investments	47.9	85.2
Investment-type insurance contracts	(24,231.2)	(25,164.2)
Long-term debt	(44.9)	(29.7)
Separate account liabilities	(112,489.0)	(72,173.8)
Carrying amount
Assets (liabilities)
Mortgage loans	11,868.1	11,519.7
Policy loans	859.6	864.9
Other investments	183.4	280.1
Cash and cash equivalents not required to be reported at fair value	1,117.1	2,404.6
Investment-type insurance contracts	(30,394.9)	(31,953.1)
Short-term debt	(175.5)	(40.8)
Long-term debt	(2,593.3)	(2,671.3)
Separate account liabilities	(113,916.9)	(73,096.0)
Bank deposits	(1,898.6)	(2,174.7)
Cash collateral payable	(30.0)	(205.6)
Fair Value
Assets (liabilities)
Mortgage loans	12,190.9	12,163.7
Policy loans	988.6	1,056.8
Other investments	184.2	280.5
Cash and cash equivalents not required to be reported at fair value	1,117.1	2,404.6
Investment-type insurance contracts	(30,627.9)	(32,531.6)
Short-term debt	(175.5)	(40.8)
Long-term debt	(2,721.9)	(2,951.4)
Separate account liabilities	(112,489.0)	(72,173.8)
Bank deposits	(1,901.7)	(2,177.7)
Cash collateral payable	$ (30.0)	$ (205.6)