Reconciliations of Changes in Level Three Assets Measured at Fair Value (Detail) (USD $) In Millions, unless otherwise specified	3 Months Ended		6 Months Ended
	Jun. 30, 2013		Jun. 30, 2013
Fair Value, Assets and Liabilities Measured on Recurring Basis, Unobservable Input Reconciliation [Line Items]
Balance as of January 1, 2013			$ 214.3
Net realized/unrealized gains included in:
Net earnings			0.9	[1]
Other comprehensive income			3.4
Purchases			109.8
Sales			(24.5)
Issuances
Settlements			(21.0)
Transfers into Level 3	21.7		21.7	[2]
Transfers out of Level 3
Balance as of June 30, 2013	304.6		304.6
Debt Securities | U.S. corporate bonds
Fair Value, Assets and Liabilities Measured on Recurring Basis, Unobservable Input Reconciliation [Line Items]
Balance as of January 1, 2013			30.4
Net realized/unrealized gains included in:
Net earnings			0.3	[1]
Other comprehensive income			(0.6)
Sales			(23.8)
Issuances
Settlements			(0.7)
Transfers out of Level 3
Balance as of June 30, 2013	5.6		5.6
Debt Securities | Mortgage and asset backed securities | RMBS
Fair Value, Assets and Liabilities Measured on Recurring Basis, Unobservable Input Reconciliation [Line Items]
Balance as of January 1, 2013			59.6
Net realized/unrealized gains included in:
Net earnings			0.3	[1]
Other comprehensive income			4.0
Issuances
Settlements			(4.5)
Transfers into Level 3			21.3	[2]
Transfers out of Level 3
Balance as of June 30, 2013	80.7		80.7
Debt Securities | Mortgage and asset backed securities | CMBS
Fair Value, Assets and Liabilities Measured on Recurring Basis, Unobservable Input Reconciliation [Line Items]
Balance as of January 1, 2013			76.1
Net realized/unrealized gains included in:
Net earnings			0.1	[1]
Other comprehensive income			(1.7)
Purchases			9.8
Sales			(0.7)
Issuances
Settlements			(5.8)
Transfers into Level 3			0.1	[2]
Transfers out of Level 3
Balance as of June 30, 2013	77.9		77.9
Debt Securities | Mortgage and asset backed securities | Other asset-backed securities
Fair Value, Assets and Liabilities Measured on Recurring Basis, Unobservable Input Reconciliation [Line Items]
Balance as of January 1, 2013			5.9
Net realized/unrealized gains included in:
Net earnings			0.2	[1]
Other comprehensive income			(0.5)
Issuances
Settlements			(4.3)
Transfers into Level 3			0.3	[2]
Transfers out of Level 3
Balance as of June 30, 2013	1.6		1.6
Other invested assets
Fair Value, Assets and Liabilities Measured on Recurring Basis, Unobservable Input Reconciliation [Line Items]
Balance as of January 1, 2013			42.3	[3]
Net realized/unrealized gains included in:
Other comprehensive income			2.2	[3]
Purchases			100.0	[3]
Issuances				[3]
Settlements			(5.7)	[3]
Transfers out of Level 3				[3]
Balance as of June 30, 2013	$ 138.8	[3]	$ 138.8	[3]

[1] There were no other than temporary impairment ("OTTI") losses recorded in net earnings related to Level 3 instruments still held as of June 30, 2013.

[2] Principally due to a decrease in observable inputs related to the valuation of such securities.

[3] Includes partnership and non-marketable equity investments accounted for on an AFS basis.