Fair Value Summary of Quantitative Information about Level 3 Fair Value Measurements (Detail) (USD $)	6 Months Ended				12 Months Ended
	Jun. 30, 2014 Investment		Jun. 30, 2013 Investment		Dec. 31, 2013 Investment
Fair Value Inputs, Assets, Quantitative Information [Line Items]
Fair Value	$ 18,759,200,000	[1],[2]	$ 17,486,400,000	[1],[2]	$ 18,054,700,000	[1],[2]
Fair Value, Inputs, Level 3
Fair Value Inputs, Assets, Quantitative Information [Line Items]
Fair Value	71,900,000		258,200,000		68,700,000
External Pricing | Fair Value, Inputs, Level 3 | Fixed maturities
Fair Value Inputs, Assets, Quantitative Information [Line Items]
Fair Value	27,600,000		41,500,000		29,200,000
External Pricing | Fair Value, Inputs, Level 3 | Fixed maturities | Asset-backed Securities | Residential mortgage-backed securities
Fair Value Inputs, Assets, Quantitative Information [Line Items]
Fair Value	0
External Pricing | Fair Value, Inputs, Level 3 | Fixed maturities | Asset-backed Securities | Residential mortgage-backed securities | Prepayment Rate Zero Percent [Member]
Fair Value Inputs, Assets, Quantitative Information [Line Items]
Number of securities			1		1
Fair Value			13,900,000		200,000
Valuation Technique			External vendor		External vendor
Unobservable Input, prepayment rate			0.00%		0.00%
External Pricing | Fair Value, Inputs, Level 3 | Fixed maturities | Asset-backed Securities | Residential mortgage-backed securities | Prepayment Rate One Percent
Fair Value Inputs, Assets, Quantitative Information [Line Items]
Number of securities			1
Fair Value			13,900,000
Valuation Technique			External vendor
Unobservable Input, prepayment rate			1.00%
External Pricing | Fair Value, Inputs, Level 3 | Fixed maturities | Asset-backed Securities | Commercial mortgage-backed securities | Prepayment Rate Zero Percent [Member]
Fair Value Inputs, Assets, Quantitative Information [Line Items]
Number of securities	2		2		2
Fair Value	27,600,000		27,600,000		29,000,000
Valuation Technique	External vendor		External vendor		External vendor
Unobservable Input, prepayment rate	0.00%		0.00%		0.00%
Internal Pricing | Fair Value, Inputs, Level 3 | Fixed maturities
Fair Value Inputs, Assets, Quantitative Information [Line Items]
Number of securities	0		0		0
Internal Pricing | Fair Value, Inputs, Level 3 | Equity securities | Nonredeemable preferred stocks
Fair Value Inputs, Assets, Quantitative Information [Line Items]
Number of securities	1		1		1
Fair Value	43,800,000		34,800,000		39,000,000
Internal Pricing | Fair Value, Inputs, Level 3 | Equity securities | Nonredeemable preferred stocks | Financials
Fair Value Inputs, Assets, Quantitative Information [Line Items]
Fair Value	43,800,000		34,800,000		39,000,000
Valuation Technique	Multiple of tangible net book value		Multiple of tangible net book value		Multiple of tangible net book value
Unobservable Input, price to book ratio multiple	1.9		1.9		1.9
Internal Pricing | Fair Value, Inputs, Level 3 | Equity securities | Common equities
Fair Value Inputs, Assets, Quantitative Information [Line Items]
Number of securities	0		1		0
Fair Value			38,000,000
Subtotal Level 3 Securities | Fair Value, Inputs, Level 3
Fair Value Inputs, Assets, Quantitative Information [Line Items]
Fair Value	71,400,000		76,300,000		68,200,000
Third Party Pricing Exemption Securities | Fair Value, Inputs, Level 3
Fair Value Inputs, Assets, Quantitative Information [Line Items]
Fair Value	500,000	[3]	181,900,000	[4]	500,000	[3]
Third Party Pricing Exemption Securities | Fair Value, Inputs, Level 3 | Other Non Binding Externally Priced Securities
Fair Value Inputs, Assets, Quantitative Information [Line Items]
Fair Value			143,900,000
Third Party Pricing Exemption Securities | Fair Value, Inputs, Level 3 | Equity securities
Fair Value Inputs, Assets, Quantitative Information [Line Items]
Fair Value			$ 38,000,000

[1] Our portfolio reflects the effect of unsettled security transactions and collateral on open derivative positions; at June 30, 2014, $235.8 million was included in "other liabilities," compared to $117.0 million and $61.3 million at June 30, 2013 and December 31, 2013, respectively.

[2] The total fair value of the portfolio at June 30, 2014 and 2013, and December 31, 2013 included $1.1 billion, $1.2 billion, and $1.8 billion, respectively, of securities held in a consolidated, non-insurance subsidiary of the holding company, net of any unsettled security transactions.

[3] The fair values for these securities were obtained from non-binding external sources where unobservable inputs are not reasonably available to us.

[4] The fair values for $143.9 million of these securities were obtained from non-binding external sources where unobservable inputs are not reasonably available to us. The remaining $38.0 million reflects a negotiated sale on a private common equity security that was completed by the end of 2013.