Fair Value Measurements (Details 7) - USD ($) $ in Millions	Jun. 30, 2015	Dec. 31, 2014
Assets (liabilities)
Mortgage loans	$ 12,070.7	$ 11,811.6
Policy loans	824.9	829.2
Short-term debt	(26.6)	(28.0)
Long-term debt	(3,315.9)	(2,531.2)
Fair value hierarchy Level 1
Assets (liabilities)
Cash and cash equivalents not required to be reported at fair value	823.4	822.2
Bank deposits	(1,370.9)	(1,343.8)
Cash collateral payable	(86.9)	(148.3)
Fair value hierarchy Level 2
Assets (liabilities)
Other investments	180.4	183.7
Investment-type insurance contracts	(5,239.4)	(5,455.4)
Short-term debt	(26.6)	(28.0)
Long-term debt	(3,369.7)	(2,703.8)
Bank deposits	(621.9)	(641.7)
Fair value hierarchy Level 3
Assets (liabilities)
Mortgage loans	12,509.8	12,350.2
Policy loans	1,014.5	1,083.2
Other investments	80.9	27.9
Investment-type insurance contracts	(22,283.4)	(22,867.3)
Long-term debt	(68.1)	(82.3)
Separate account liabilities	(129,743.4)	(127,131.0)
Carrying amount
Assets (liabilities)
Mortgage loans	12,070.7	11,811.6
Policy loans	824.9	829.2
Other investments	250.3	211.2
Cash and cash equivalents not required to be reported at fair value	823.4	822.2
Investment-type insurance contracts	(27,548.1)	(28,256.3)
Short-term debt	(26.6)	(28.0)
Long-term debt	(3,315.9)	(2,531.2)
Separate account liabilities	(131,065.0)	(128,480.5)
Bank deposits	(1,987.9)	(1,979.7)
Cash collateral payable	(86.9)	(148.3)
Assets (liabilities) measured at fair value
Assets (liabilities)
Mortgage loans	12,509.8	12,350.2
Policy loans	1,014.5	1,083.2
Other investments	261.3	211.6
Cash and cash equivalents not required to be reported at fair value	823.4	822.2
Investment-type insurance contracts	(27,522.7)	(28,322.7)
Short-term debt	(26.6)	(28.0)
Long-term debt	(3,437.8)	(2,786.1)
Separate account liabilities	(129,743.4)	(127,131.0)
Bank deposits	(1,992.8)	(1,985.5)
Cash collateral payable	$ (86.9)	$ (148.3)