Investments - Additional Information (Detail) (USD $)	3 Months Ended		6 Months Ended		12 Months Ended
	Jun. 30, 2014	Jun. 30, 2013	Jun. 30, 2014	Jun. 30, 2013	Dec. 31, 2013
Schedule of Investments
Fair value of fixed maturity securities	$ 44,900,900,000		$ 44,900,900,000		$ 42,344,400,000
Fair value of fixed maturity securities, gross unrealized gain			6,081,100,000		4,358,700,000
Fair Value of fixed maturity securities, gross unrealized loss			65,000,000		303,900,000
Fixed Maturity Securities Other Than Temporary Impairments in Accumulated Other Comprehensive Income Loss	0		0		0
Commitment to fund private placement fixed maturity securities	137,600,000		137,600,000
Carrying amount of variable interest entity investments	484,600,000		484,600,000
Unfunded commitment to fund Investment Partnerships	15,700,000		15,700,000
Commitment to fund partnership Equity Investments	135,500,000		135,500,000
Other Long-term Investments	570,800,000		570,800,000		566,000,000
Commitments to Fund Special Purpose Entities	0		0
Amount Funded to Special Purpose Entity Partnerships	nor did we fund any amounts to the partnership	nor did we fund any amounts to the partnerships	nor did we fund any amounts to the partnership	nor did we fund any amounts to the partnership
Mortgage Loan policy is not to exceed a loan-to-value ratio, percent	75.00%		75.00%
Loan to Value Ratio Update Frequency			3 years
Mortgage Loan Inspection Frequency			2 years
Mortage Loan Policy Debt Service coverage ratio lower range	125.00%		125.00%
Mortgage Loans issuance, term years	25		25
Number of Changes to Accounting Policy for Estimating Credit Losses on Mortgage Loans			0
Recorded Investment in Financing Receivables on Nonaccrual Status	18,100,000		18,100,000
Number of Financing Receivables on Nonaccrual Status	1		1		0
Average Recorded Investment in Impaired Financing Receivable	31,200,000	16,000,000	25,200,000	16,700,000
Interest Income on Impaired Financing Receivable, Accrual Method	400,000	200,000	700,000	400,000
Committments to Fund Commercial Mortgage Loans	18,400,000		18,400,000
Repurchase agreements - Typical Days outstanding			30
Minimum percent of the fair value of securities loaned or securities purchased under repurchase agreements be maintained as collateral	102.00%		102.00%
Fixed Maturity Securities Loaned to Third Parties	176,900,000		176,900,000		201,600,000
Collateral Received in Form of Cash	57,400,000		57,400,000		76,500,000
Securities Received as Collateral	125,100,000		125,100,000		132,900,000
Outstanding Repurchase Agreements	0		0		0
Special Purpose Entity | Bonds
Schedule of Investments
Fair value of fixed maturity securities	140,800,000		140,800,000
Special Purpose Entity | Partnership Interest
Schedule of Investments
Other Long-term Investments	1,900,000		1,900,000
Partnership Interests In Tax Credit Investments
Schedule of Investments
Carrying amount of variable interest entity investments	300,100,000		300,100,000
Equity Method Investments
Schedule of Investments
Carrying amount of variable interest entity investments	184,500,000		184,500,000
External Credit Rating, Investment Grade
Schedule of Investments
Fair value of fixed maturity securities	41,459,800,000		41,459,800,000
Fair value of fixed maturity securities, gross unrealized gain			5,853,500,000
Fair Value of fixed maturity securities, gross unrealized loss			50,300,000
Fixed maturity securities in unrealized loss position, percent of total	77.40%		77.40%
Number of fixed maturity securities that were in an unrealized loss position	80		80
Number of fixed maturity securities in an unrealized loss position continuously for over one year	71		71
External Credit Rating, Non Investment Grade
Schedule of Investments
Fair value of fixed maturity securities	3,441,100,000		3,441,100,000
Fair value of fixed maturity securities, gross unrealized gain			227,600,000
Fair Value of fixed maturity securities, gross unrealized loss			$ 14,700,000
Fixed maturity securities in unrealized loss position, percent of total	22.60%		22.60%
Number of fixed maturity securities that were in an unrealized loss position	21		21
Number of fixed maturity securities in an unrealized loss position continuously for over one year	18		18