Fair Value Measurements Other Financial Instruments (Details) (USD $) In Millions, unless otherwise specified	Dec. 31, 2013		Dec. 31, 2012
Fair Value, Balance Sheet Grouping, Financial Statement Captions [Line Items]
Investments	$ 20,700.6		$ 21,378.3
Derivative assets	464.4		512.7
Derivatives liabilities	216.6		346.8
Carrying Value
Fair Value, Balance Sheet Grouping, Financial Statement Captions [Line Items]
Limited partnerships/corporations	180.9		179.6
Cash and cash equivalents, short-term investments and short-term investments under securirites loan agreement	529.7		1,229.3
Derivative assets	464.4		512.7
Notes receivable from affiliates	175.0		175.0
Assets held in separate accounts	60,104.9		53,655.3
Derivatives liabilities	216.6		346.8
Long-term debt, fair value	4.9		4.9
Total
Fair Value, Balance Sheet Grouping, Financial Statement Captions [Line Items]
Limited partnerships/corporations	180.9		179.6
Cash and cash equivalents, short-term investments and short-term investments under securirites loan agreement	529.7		1,229.3
Derivative assets	464.4		512.7
Notes receivable from affiliates	186.4		194.3
Assets held in separate accounts	60,104.9		53,655.3
Derivatives liabilities	216.6		346.8
Long-term debt, fair value	4.9		4.9
Funding agreements without fixed maturities and deferred annuities(1) | Carrying Value
Fair Value, Balance Sheet Grouping, Financial Statement Captions [Line Items]
Liabilities	21,010.8	[1]	20,263.4	[1]
Funding agreements without fixed maturities and deferred annuities(1) | Total
Fair Value, Balance Sheet Grouping, Financial Statement Captions [Line Items]
Liabilities	24,379.6	[1]	25,156.5	[1]
Supplementary contracts, immediate annuities and other | Carrying Value
Fair Value, Balance Sheet Grouping, Financial Statement Captions [Line Items]
Liabilities	624.3		680.0
Supplementary contracts, immediate annuities and other | Total
Fair Value, Balance Sheet Grouping, Financial Statement Captions [Line Items]
Liabilities	727.1		837.3
FIA | Carrying Value
Fair Value, Balance Sheet Grouping, Financial Statement Captions [Line Items]
Liabilities	23.1		20.4
FIA | Total
Fair Value, Balance Sheet Grouping, Financial Statement Captions [Line Items]
Liabilities	23.1		20.4
Stabilizer and MCGs | Carrying Value
Fair Value, Balance Sheet Grouping, Financial Statement Captions [Line Items]
Liabilities	0		102.0
Stabilizer and MCGs | Total
Fair Value, Balance Sheet Grouping, Financial Statement Captions [Line Items]
Liabilities	0		102.0
Mortgage loans on real estate | Carrying Value
Fair Value, Balance Sheet Grouping, Financial Statement Captions [Line Items]
Loans	3,396.1		2,872.7
Mortgage loans on real estate | Total
Fair Value, Balance Sheet Grouping, Financial Statement Captions [Line Items]
Loans	3,403.9		2,946.9
Policy loans | Carrying Value
Fair Value, Balance Sheet Grouping, Financial Statement Captions [Line Items]
Loans	242.0		240.9
Policy loans | Total
Fair Value, Balance Sheet Grouping, Financial Statement Captions [Line Items]
Loans	242.0		240.9
Fixed maturities, available-for-sale, including securities pledged | Carrying Value
Fair Value, Balance Sheet Grouping, Financial Statement Captions [Line Items]
Investments	20,705.8		21,455.2
Fixed maturities, available-for-sale, including securities pledged | Total
Fair Value, Balance Sheet Grouping, Financial Statement Captions [Line Items]
Investments	20,705.8		21,455.2
Equity securities, available-for-sale | Carrying Value
Fair Value, Balance Sheet Grouping, Financial Statement Captions [Line Items]
Investments	134.9		142.8
Equity securities, available-for-sale | Total
Fair Value, Balance Sheet Grouping, Financial Statement Captions [Line Items]
Investments	134.9		142.8
Embedded derivative on reinsurance | Carrying Value
Fair Value, Balance Sheet Grouping, Financial Statement Captions [Line Items]
Derivatives liabilities	(54.0)		0
Embedded derivative on reinsurance | Total
Fair Value, Balance Sheet Grouping, Financial Statement Captions [Line Items]
Derivatives liabilities	$ (54.0)		$ 0

[1] Certain amounts included in Funding agreements without fixed maturities and deferred annuities are also reflected within the Annuity product guarantees section of the table above.