Derivative Financial Instruments (Details) (USD $) In Millions, unless otherwise specified	3 Months Ended
	Mar. 31, 2014	Dec. 31, 2013
Derivative Financial Instruments, exposure
GMWB minimum account balance to make withdrawals by customer	$ 0
Cash and securities posted under collateral arrangements associated with derivative credit support agreements and Futures Commission Merchant agreements	320.4	393.1
Aggregate fair value of all derivative instruments with credit-risk-related contingent features that were in a liability position	912.6	1,042.9
Collateral and initial margin posted supporting derivatives with credit-risk-related contingent features that were in a liability position	320.4	393.1
Additional collateral required to be posted if derivative credit-risk-related contingent features were triggered	78.0
Cash collateral received associated with derivative credit support annex agreements and Futures Commission Merchant agreements	37.6	32.5
Notional amount	37,920.9	38,840.3
Gross credit exposure	645.2	720.1
Less: collateral received	92.2	115.9
Net credit exposure	553.0	604.2
Interest rate swaps
Derivative Financial Instruments, exposure
Cash exchanged under contract	0
Principal payments made under contract	0
Notional amount	19,641.9	20,570.8
Gross credit exposure	435.0	435.5
Interest rate options
Derivative Financial Instruments, exposure
Notional amount	4,100.0	4,100.0
Gross credit exposure	34.9	42.5
Swaptions
Derivative Financial Instruments, exposure
Notional amount	260.0	325.0
Gross credit exposure	0.4	1.0
Interest rate futures
Derivative Financial Instruments, exposure
Notional amount	120.5	92.5
Currency swaps
Derivative Financial Instruments, exposure
Notional amount	2,051.3	2,367.5
Gross credit exposure	147.5	200.9
Currency forwards
Derivative Financial Instruments, exposure
Notional amount	261.8	247.4
Gross credit exposure		0.6
Equity options
Derivative Financial Instruments, exposure
Notional amount	2,160.9	2,010.4
Gross credit exposure	17.7	30.0
Equity futures
Derivative Financial Instruments, exposure
Notional amount	325.2	273.3
Credit default swaps
Derivative Financial Instruments, exposure
Notional amount	1,162.1	1,153.2
Gross credit exposure	9.7	9.5
Total return swaps
Derivative Financial Instruments, exposure
Notional amount	90.0	90.0
Gross credit exposure		0.1
Credit Futures
Derivative Financial Instruments, exposure
Notional amount	11.0	9.1
Embedded derivative financial instruments
Derivative Financial Instruments, exposure
Notional amount	$ 7,736.2	$ 7,601.1