Condensed Consolidating Financial Information - Statements of Cash Flows (Details) (USD $) In Millions, unless otherwise specified	3 Months Ended
	Mar. 31, 2014	Mar. 31, 2013
Condensed Financial Statements, Captions [Line Items]
Net cash provided by (used in) operating activities	$ 786.6	$ (28.4)
Proceeds from the sale, maturity, disposal or redemption of:
Fixed maturities	2,629.7	4,455.8
Equity securities, available-for-sale	47.7	28.4
Mortgage loans on real estate	307.4	318.3
Limited partnerships/corporations	60.9	18.0
Acquisition of:
Fixed maturities	(3,057.2)	(4,802.8)
Equity securities, available-for-sale	(7.4)	(9.4)
Mortgage loans on real estate	(252.9)	(581.4)
Limited partnerships/corporations	(18.4)	(9.8)
Short-term investments, net	1.9	2,999.1
Policy loans, net	27.3	(4.1)
Derivatives, net	(178.6)	(1,089.6)
Other investments, net	2.0	11.8
Sales from consolidated investment entities	571.8	573.8
Purchases within consolidated investment entities	(1,258.8)	(613.8)
Maturity of intercompany loans issued to subsidiaries with maturities more than three months	0
Net (issuance) maturity of short-term intercompany loans	0	0
Return of capital contributions from subsidiaries	0
Capital contributions to subsidiaries	0
Collateral received (delivered), net	89.4	(360.5)
Purchases of fixed assets, net	(8.7)	(6.6)
Other, net	0
Net cash (used in) provided by investing activities	(1,043.9)	927.2
Cash Flows from Financing Activities:
Deposits received for investment contracts	2,500.0	2,936.2
Maturities and withdrawals from investment contracts	(2,809.7)	(2,996.6)
Proceeds from issuance of debt with maturities of more than three months	0	(1,000.6)
Repayment of debt with maturities of more than three months	0	(1,304.6)
Short-term debt, net	0	169.7
Debt issuance costs	(16.7)	(6.5)
Intercompany loans with maturities of more than three months	0
Net (repayments of) proceeds from short-term intercompany loans	0	0
Dividends to parent	0	0
Return of capital contributions to parent	0
Contributions of capital from parent	0
Borrowings of consolidated investment entities	(28.4)	0
Contributions from (distributions to) participants in consolidated investment entities	466.9	642.7
Common stock acquired - Share buyback	(250.0)	0
Dividends paid	(2.6)	0
Net cash (used in) provided by financing activities	(83.7)	102.1
Net (decrease) increase in cash and cash equivalents	(341.0)	1,000.9
Cash and cash equivalents, beginning of year	2,840.8	1,786.8
Cash and cash equivalents, end of year	2,499.8	2,787.7
Parent Issuer
Condensed Financial Statements, Captions [Line Items]
Net cash provided by (used in) operating activities	(12.1)	152.3
Proceeds from the sale, maturity, disposal or redemption of:
Fixed maturities	0	0
Equity securities, available-for-sale	2.4	3.2
Mortgage loans on real estate	0	0
Limited partnerships/corporations	0	0
Acquisition of:
Fixed maturities	0	0
Equity securities, available-for-sale	(6.5)	(5.2)
Mortgage loans on real estate	0	0
Limited partnerships/corporations	0	0
Short-term investments, net	(21.0)	0
Policy loans, net	0	0
Derivatives, net	11.5	0
Other investments, net	0	0
Sales from consolidated investment entities	0	0
Purchases within consolidated investment entities	0	0
Maturity of intercompany loans issued to subsidiaries with maturities more than three months	0.6
Net (issuance) maturity of short-term intercompany loans	(159.3)	(34.9)
Return of capital contributions from subsidiaries	75.0
Capital contributions to subsidiaries	0
Collateral received (delivered), net	0	8.6
Purchases of fixed assets, net	0	0
Other, net	0
Net cash (used in) provided by investing activities	(97.3)	(28.3)
Cash Flows from Financing Activities:
Deposits received for investment contracts	0	0
Maturities and withdrawals from investment contracts	0	0
Proceeds from issuance of debt with maturities of more than three months		(1,000.3)
Repayment of debt with maturities of more than three months		(945.3)
Short-term debt, net		169.7
Debt issuance costs	(16.7)	(6.5)
Intercompany loans with maturities of more than three months	0
Net (repayments of) proceeds from short-term intercompany loans	180.0	23.9
Dividends to parent	0	0
Return of capital contributions to parent	0
Contributions of capital from parent	0
Borrowings of consolidated investment entities	0
Contributions from (distributions to) participants in consolidated investment entities	0	0
Common stock acquired - Share buyback	(250.0)
Dividends paid	(2.6)
Net cash (used in) provided by financing activities	(89.3)	(97.3)
Net (decrease) increase in cash and cash equivalents	(198.7)	26.7
Cash and cash equivalents, beginning of year	640.2	357.5
Cash and cash equivalents, end of year	441.5	384.2
Subsidiary Guarantor
Condensed Financial Statements, Captions [Line Items]
Net cash provided by (used in) operating activities	8.0	(2.0)
Proceeds from the sale, maturity, disposal or redemption of:
Fixed maturities	0	0
Equity securities, available-for-sale	13.1	12.4
Mortgage loans on real estate	0	0
Limited partnerships/corporations	0	0
Acquisition of:
Fixed maturities	0	0
Equity securities, available-for-sale	0	0
Mortgage loans on real estate	0	0
Limited partnerships/corporations	0	0
Short-term investments, net	0	0
Policy loans, net	0	0
Derivatives, net	0	0
Other investments, net	0	0
Sales from consolidated investment entities	0	0
Purchases within consolidated investment entities	0	0
Maturity of intercompany loans issued to subsidiaries with maturities more than three months	0
Net (issuance) maturity of short-term intercompany loans	0	(10.5)
Return of capital contributions from subsidiaries	0
Capital contributions to subsidiaries	(156.0)
Collateral received (delivered), net	0	0
Purchases of fixed assets, net	0	0
Other, net	0.2
Net cash (used in) provided by investing activities	(142.7)	1.9
Cash Flows from Financing Activities:
Deposits received for investment contracts	0	0
Maturities and withdrawals from investment contracts	0	0
Proceeds from issuance of debt with maturities of more than three months		0
Repayment of debt with maturities of more than three months		0
Short-term debt, net		0
Debt issuance costs	0	0
Intercompany loans with maturities of more than three months	0
Net (repayments of) proceeds from short-term intercompany loans	135.1	0
Dividends to parent	0	0
Return of capital contributions to parent	0
Contributions of capital from parent	0
Borrowings of consolidated investment entities	0
Contributions from (distributions to) participants in consolidated investment entities	0	0
Common stock acquired - Share buyback	0
Dividends paid	0
Net cash (used in) provided by financing activities	135.1	0
Net (decrease) increase in cash and cash equivalents	0.4	(0.1)
Cash and cash equivalents, beginning of year	1.1	0.4
Cash and cash equivalents, end of year	1.5	0.3
Non-Guarantor Subsidiaries
Condensed Financial Statements, Captions [Line Items]
Net cash provided by (used in) operating activities	816.7	(163.7)
Proceeds from the sale, maturity, disposal or redemption of:
Fixed maturities	2,629.7	4,455.8
Equity securities, available-for-sale	32.2	12.8
Mortgage loans on real estate	307.4	318.3
Limited partnerships/corporations	60.9	18.0
Acquisition of:
Fixed maturities	(3,057.2)	(4,802.8)
Equity securities, available-for-sale	(0.9)	(4.2)
Mortgage loans on real estate	(252.9)	(581.4)
Limited partnerships/corporations	(18.4)	(9.8)
Short-term investments, net	22.9	2,999.1
Policy loans, net	27.3	(4.1)
Derivatives, net	(190.1)	(1,089.6)
Other investments, net	2.0	11.8
Sales from consolidated investment entities	571.8	573.8
Purchases within consolidated investment entities	(1,258.8)	(613.8)
Maturity of intercompany loans issued to subsidiaries with maturities more than three months	0
Net (issuance) maturity of short-term intercompany loans	(180.0)	(13.4)
Return of capital contributions from subsidiaries	0
Capital contributions to subsidiaries	0
Collateral received (delivered), net	89.4	(369.1)
Purchases of fixed assets, net	(8.7)	(6.6)
Other, net	(0.2)
Net cash (used in) provided by investing activities	(1,223.6)	894.8
Cash Flows from Financing Activities:
Deposits received for investment contracts	2,500.0	2,936.2
Maturities and withdrawals from investment contracts	(2,809.7)	(2,996.6)
Proceeds from issuance of debt with maturities of more than three months		(0.3)
Repayment of debt with maturities of more than three months		(359.3)
Short-term debt, net		0
Debt issuance costs	0	0
Intercompany loans with maturities of more than three months	(0.6)
Net (repayments of) proceeds from short-term intercompany loans	24.2	34.9
Dividends to parent	(26.0)	(15.0)
Return of capital contributions to parent	(75.0)
Contributions of capital from parent	156.0
Borrowings of consolidated investment entities	(28.4)
Contributions from (distributions to) participants in consolidated investment entities	466.9	642.7
Common stock acquired - Share buyback	0
Dividends paid	0
Net cash (used in) provided by financing activities	264.2	243.2
Net (decrease) increase in cash and cash equivalents	(142.7)	974.3
Cash and cash equivalents, beginning of year	2,199.5	1,428.9
Cash and cash equivalents, end of year	2,056.8	2,403.2
Consolidating Adjustments
Condensed Financial Statements, Captions [Line Items]
Net cash provided by (used in) operating activities	(26.0)	(15.0)
Proceeds from the sale, maturity, disposal or redemption of:
Fixed maturities	0	0
Equity securities, available-for-sale	0	0
Mortgage loans on real estate	0	0
Limited partnerships/corporations	0	0
Acquisition of:
Fixed maturities	0	0
Equity securities, available-for-sale	0	0
Mortgage loans on real estate	0	0
Limited partnerships/corporations	0	0
Short-term investments, net	0	0
Policy loans, net	0	0
Derivatives, net	0	0
Other investments, net	0	0
Sales from consolidated investment entities	0	0
Purchases within consolidated investment entities	0	0
Maturity of intercompany loans issued to subsidiaries with maturities more than three months	(0.6)
Net (issuance) maturity of short-term intercompany loans	339.3	58.8
Return of capital contributions from subsidiaries	(75.0)
Capital contributions to subsidiaries	156.0
Collateral received (delivered), net	0	0
Purchases of fixed assets, net	0	0
Other, net	0
Net cash (used in) provided by investing activities	419.7	58.8
Cash Flows from Financing Activities:
Deposits received for investment contracts	0	0
Maturities and withdrawals from investment contracts	0	0
Proceeds from issuance of debt with maturities of more than three months		0
Repayment of debt with maturities of more than three months		0
Short-term debt, net		0
Debt issuance costs	0	0
Intercompany loans with maturities of more than three months	0.6
Net (repayments of) proceeds from short-term intercompany loans	(339.3)	(58.8)
Dividends to parent	26.0	15.0
Return of capital contributions to parent	75.0
Contributions of capital from parent	(156.0)
Borrowings of consolidated investment entities	0
Contributions from (distributions to) participants in consolidated investment entities	0	0
Common stock acquired - Share buyback	0
Dividends paid	0
Net cash (used in) provided by financing activities	(393.7)	(43.8)
Net (decrease) increase in cash and cash equivalents	0	0
Cash and cash equivalents, beginning of year	0	0
Cash and cash equivalents, end of year	$ 0	$ 0