Condensed Consolidating Financial Information - Statements of Cash Flows (Details) (USD $) In Millions, unless otherwise specified	9 Months Ended
	Sep. 30, 2014	Sep. 30, 2013
Condensed Financial Statements, Captions [Line Items]
Net cash provided by operating activities	$ 2,916.2	$ 2,942.1
Proceeds from the sale, maturity, disposal or redemption of:
Fixed maturities	9,192.3	11,626.7
Equity securities, available-for-sale	63.7	47.1
Mortgage loans on real estate	937.6	1,253.5
Limited partnerships/corporations	137.6	274.8
Acquisition of:
Fixed maturities	(9,172.3)	(14,281.7)
Equity securities, available-for-sale	(18.3)	(17.9)
Mortgage loans on real estate	(1,574.8)	(1,583.2)
Limited partnerships/corporations	(261.3)	(81.0)
Short-term investments, net	(124.5)	3,443.2
Policy loans, net	42.8	52.8
Derivatives, net	(670.7)	(1,981.6)
Other investments, net	38.5	34.3
Sales from consolidated investment entities	2,558.5	2,518.7
Purchases within consolidated investment entities	(4,292.6)	(3,352.2)
Maturity of intercompany loans issued to subsidiaries with maturities more than three months	0	0
Net (issuance) maturity of short-term intercompany loans	0	0
Return of capital contributions from subsidiaries	0	0
Capital contributions to subsidiaries	0	0
Collateral received (delivered), net	116.8	(751.5)
Purchases of fixed assets, net	(26.5)	(25.7)
Net cash used in investing activities	(3,053.2)	(2,823.7)
Cash Flows from Financing Activities:
Deposits received for investment contracts	5,681.5	8,985.2
Maturities and withdrawals from investment contracts	(7,332.9)	(9,648.9)
Proceeds from issuance of debt with maturities of more than three months	0	2,147.1
Repayment of debt with maturities of more than three months	0	(2,697.4)
Short-term debt, net	0	171.6
Debt issuance costs	(16.8)	(24.8)
Intercompany loans with maturities of more than three months	0	0
Net (repayments of) proceeds from short-term intercompany loans	0	0
Dividends to parent	0	0
Return of capital contributions to parent	0	0
Contributions of capital from parent	0	0
Borrowings of consolidated investment entities	340.5	32.0
Repayments of borrowings of consolidated investment entities	(66.6)	(8.5)
Contributions from (distributions to) participants in consolidated investment entities, net	1,235.9	626.7
Proceeds from issuance of common stock, net	0	571.6
Common stock acquired - Share repurchase	(614.4)	0
Share-based compensation	(14.8)	0
Dividends paid	(7.7)	0
Net cash used in financing activities	(795.3)	(188.6)
Net decrease in cash and cash equivalents	(932.3)	(70.2)
Cash and cash equivalents, beginning of year	2,840.8	1,786.8
Cash and cash equivalents, end of year	1,908.5	1,716.6
Parent Issuer
Condensed Financial Statements, Captions [Line Items]
Net cash provided by operating activities	(163.3)	162.4
Proceeds from the sale, maturity, disposal or redemption of:
Fixed maturities	0	0
Equity securities, available-for-sale	13.0	9.9
Mortgage loans on real estate	0	0
Limited partnerships/corporations	0	0
Acquisition of:
Fixed maturities	0	0
Equity securities, available-for-sale	(15.6)	(10.5)
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	1.4	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	0.8	2.3
Net (issuance) maturity of short-term intercompany loans	4.2	(274.5)
Return of capital contributions from subsidiaries	797.0	1,434.0
Capital contributions to subsidiaries	(150.0)	(2,062.0)
Collateral received (delivered), net	0	12.7
Purchases of fixed assets, net	0	0
Net cash used in investing activities	650.8	(888.1)
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		2,146.8
Repayment of debt with maturities of more than three months		(1,370.3)
Short-term debt, net		171.7
Debt issuance costs	(16.8)	(24.8)
Intercompany loans with maturities of more than three months	0	0
Net (repayments of) proceeds from short-term intercompany loans	0	(319.1)
Dividends to parent	0	0
Return of capital contributions to parent	0	0
Contributions of capital from parent	0	0
Borrowings of consolidated investment entities	0	0
Repayments of borrowings of consolidated investment entities	0	0
Contributions from (distributions to) participants in consolidated investment entities, net	0	0
Proceeds from issuance of common stock, net		571.6
Common stock acquired - Share repurchase	(614.4)
Share-based compensation	(14.8)
Dividends paid	(7.7)
Net cash used in financing activities	(653.7)	832.5
Net decrease in cash and cash equivalents	(166.2)	106.8
Cash and cash equivalents, beginning of year	640.2	357.5
Cash and cash equivalents, end of year	474.0	464.3
Subsidiary Guarantor
Condensed Financial Statements, Captions [Line Items]
Net cash provided by operating activities	97.2	33.8
Proceeds from the sale, maturity, disposal or redemption of:
Fixed maturities	0	0
Equity securities, available-for-sale	13.0	13.7
Mortgage loans on real estate	0	0.4
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	0.8	(0.4)
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	0
Net (issuance) maturity of short-term intercompany loans	0	58.0
Return of capital contributions from subsidiaries	690.0	987.0
Capital contributions to subsidiaries	(171.0)	0
Collateral received (delivered), net	0	0
Purchases of fixed assets, net	0	0
Net cash used in investing activities	532.8	1,058.7
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		(638.6)
Short-term debt, net		0
Debt issuance costs	0	0
Intercompany loans with maturities of more than three months	0	0
Net (repayments of) proceeds from short-term intercompany loans	62.6	253.3
Dividends to parent	0	0
Return of capital contributions to parent	(690.0)	(987.0)
Contributions of capital from parent	0	280.0
Borrowings of consolidated investment entities	0	0
Repayments of borrowings of consolidated investment entities	0	0
Contributions from (distributions to) participants in consolidated investment entities, net	0	0
Proceeds from issuance of common stock, net		0
Common stock acquired - Share repurchase	0
Share-based compensation	0
Dividends paid	0
Net cash used in financing activities	(627.4)	(1,092.3)
Net decrease in cash and cash equivalents	2.6	0.2
Cash and cash equivalents, beginning of year	1.1	0.4
Cash and cash equivalents, end of year	3.7	0.6
Non-Guarantor Subsidiaries
Condensed Financial Statements, Captions [Line Items]
Net cash provided by operating activities	3,108.3	2,807.9
Proceeds from the sale, maturity, disposal or redemption of:
Fixed maturities	9,192.3	11,626.7
Equity securities, available-for-sale	37.7	23.5
Mortgage loans on real estate	937.6	1,253.1
Limited partnerships/corporations	137.6	274.8
Acquisition of:
Fixed maturities	(9,172.3)	(14,281.7)
Equity securities, available-for-sale	(2.7)	(7.4)
Mortgage loans on real estate	(1,574.8)	(1,583.2)
Limited partnerships/corporations	(261.3)	(81.0)
Short-term investments, net	(124.5)	3,443.2
Policy loans, net	42.8	52.8
Derivatives, net	(672.1)	(1,981.6)
Other investments, net	37.7	34.7
Sales from consolidated investment entities	2,558.5	2,518.7
Purchases within consolidated investment entities	(4,292.6)	(3,352.2)
Maturity of intercompany loans issued to subsidiaries with maturities more than three months	0	0
Net (issuance) maturity of short-term intercompany loans	0	261.1
Return of capital contributions from subsidiaries	0	0
Capital contributions to subsidiaries	0	0
Collateral received (delivered), net	116.8	(764.2)
Purchases of fixed assets, net	(26.5)	(25.7)
Net cash used in investing activities	(3,065.8)	(2,588.4)
Cash Flows from Financing Activities:
Deposits received for investment contracts	5,681.5	8,985.2
Maturities and withdrawals from investment contracts	(7,332.9)	(9,648.9)
Proceeds from issuance of debt with maturities of more than three months		0.3
Repayment of debt with maturities of more than three months		(688.5)
Short-term debt, net		(0.1)
Debt issuance costs	0	0
Intercompany loans with maturities of more than three months	(0.8)	(2.3)
Net (repayments of) proceeds from short-term intercompany loans	(66.8)	21.2
Dividends to parent	(848.0)	(62.0)
Return of capital contributions to parent	(75.0)	(1,434.0)
Contributions of capital from parent	321.0	1,782.0
Borrowings of consolidated investment entities	340.5	32.0
Repayments of borrowings of consolidated investment entities	(66.6)	(8.5)
Contributions from (distributions to) participants in consolidated investment entities, net	1,235.9	626.7
Proceeds from issuance of common stock, net		0
Common stock acquired - Share repurchase	0
Share-based compensation	0
Dividends paid	0
Net cash used in financing activities	(811.2)	(396.7)
Net decrease in cash and cash equivalents	(768.7)	(177.2)
Cash and cash equivalents, beginning of year	2,199.5	1,428.9
Cash and cash equivalents, end of year	1,430.8	1,251.7
Consolidating Adjustments
Condensed Financial Statements, Captions [Line Items]
Net cash provided by operating activities	(126.0)	(62.0)
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	(0.8)	(2.3)
Net (issuance) maturity of short-term intercompany loans	(4.2)	(44.6)
Return of capital contributions from subsidiaries	(1,487.0)	(2,421.0)
Capital contributions to subsidiaries	321.0	2,062.0
Collateral received (delivered), net	0	0
Purchases of fixed assets, net	0	0
Net cash used in investing activities	(1,171.0)	(405.9)
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	0.8	2.3
Net (repayments of) proceeds from short-term intercompany loans	4.2	44.6
Dividends to parent	848.0	62.0
Return of capital contributions to parent	765.0	2,421.0
Contributions of capital from parent	(321.0)	(2,062.0)
Borrowings of consolidated investment entities	0	0
Repayments of borrowings of consolidated investment entities	0	0
Contributions from (distributions to) participants in consolidated investment entities, net	0	0
Proceeds from issuance of common stock, net		0
Common stock acquired - Share repurchase	0
Share-based compensation	0
Dividends paid	0
Net cash used in financing activities	1,297.0	467.9
Net decrease 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