Fair Value Measurements (Details 7) (USD $) In Millions, unless otherwise specified	Sep. 30, 2014	Dec. 31, 2013
Assets (liabilities)
Mortgage loans	$ 11,744.9	$ 11,533.6
Policy loans	837.7	859.7
Short-term debt	(126.3)	(150.6)
Long-term debt	(2,529.2)	(2,601.4)
Fair value hierarchy Level 1
Assets (liabilities)
Cash and cash equivalents not required to be reported at fair value	797.6	912.8
Bank deposits	(1,294.1)	(1,252.2)
Cash collateral payable	(79.6)	(32.5)
Fair value hierarchy Level 2
Assets (liabilities)
Other investments	164.6	140.9
Investment-type insurance contracts	(5,282.5)	(5,902.2)
Short-term debt	(126.3)	(150.6)
Long-term debt	(2,676.3)	(2,639.0)
Bank deposits	(659.0)	(698.9)
Fair value hierarchy Level 3
Assets (liabilities)
Mortgage loans	12,233.7	11,773.5
Policy loans	1,031.8	963.3
Other investments	30.9	33.8
Investment-type insurance contracts	(23,211.9)	(24,190.9)
Long-term debt	(80.3)	(53.1)
Separate account liabilities	(125,755.0)	(118,059.7)
Carrying amount
Assets (liabilities)
Mortgage loans	11,744.9	11,533.6
Policy loans	837.7	859.7
Other investments	195.0	174.0
Cash and cash equivalents not required to be reported at fair value	797.6	912.8
Investment-type insurance contracts	(28,371.8)	(29,909.6)
Short-term debt	(126.3)	(150.6)
Long-term debt	(2,529.2)	(2,601.4)
Separate account liabilities	(127,104.9)	(119,500.7)
Bank deposits	(1,946.7)	(1,949.0)
Cash collateral payable	(79.6)	(32.5)
Fair Value
Assets (liabilities)
Mortgage loans	12,233.7	11,773.5
Policy loans	1,031.8	963.3
Other investments	195.5	174.7
Cash and cash equivalents not required to be reported at fair value	797.6	912.8
Investment-type insurance contracts	(28,494.4)	(30,093.1)
Short-term debt	(126.3)	(150.6)
Long-term debt	(2,756.7)	(2,692.1)
Separate account liabilities	(125,755.0)	(118,059.7)
Bank deposits	(1,953.1)	(1,951.1)
Cash collateral payable	$ (79.6)	$ (32.5)