Reconciliations of Changes in Level 3 Assets Measured at Fair Value (Detail) (USD $) In Millions, unless otherwise specified	3 Months Ended		9 Months Ended
	Sep. 30, 2012		Sep. 30, 2012
Fair Value, Assets and Liabilities Measured on Recurring Basis, Unobservable Input Reconciliation [Line Items]
Beginning balance			$ 23.6
Net realized/unrealized gains included in:
Net earnings			4.6	[1]
Other comprehensive income			8.0
Purchases			147.0	[2]
Sales			(2.5)
Issuances
Settlements			(9.3)
Transfers into Level 3			41.9	[3]
Transfers out of Level 3
Ending balance	213.3		213.3
Debt Securities | Foreign government obligations
Net realized/unrealized gains included in:
Issuances
Transfers out of Level 3
Debt Securities | U.S. corporate bonds
Net realized/unrealized gains included in:
Other comprehensive income			0.5
Purchases			31.5	[2]
Issuances
Settlements			(0.7)
Transfers out of Level 3
Ending balance	31.3		31.3
Debt Securities | Mortgage and asset backed securities | RMBS
Net realized/unrealized gains included in:
Net earnings			3.7	[1]
Other comprehensive income			5.1
Purchases			55.1	[2]
Issuances
Settlements			(6.1)
Transfers out of Level 3
Ending balance	57.8		57.8
Debt Securities | Mortgage and asset backed securities | CMBS
Net realized/unrealized gains included in:
Net earnings			1.0	[1]
Purchases			37.2	[2]
Issuances
Settlements			(2.5)
Transfers into Level 3	41.9		41.9	[3]
Transfers out of Level 3
Ending balance	77.6		77.6
Debt Securities | Mortgage and asset backed securities | Other asset-backed securities
Net realized/unrealized gains included in:
Net earnings			0.1	[1]
Other comprehensive income			0.2
Purchases			6.5	[2]
Issuances
Transfers out of Level 3
Ending balance	6.8		6.8
Other invested assets
Fair Value, Assets and Liabilities Measured on Recurring Basis, Unobservable Input Reconciliation [Line Items]
Beginning balance			23.6	[4]
Net realized/unrealized gains included in:
Net earnings			(0.2)	[1],[4]
Other comprehensive income			2.2	[4]
Purchases			16.7	[2],[4]
Sales			(2.5)	[4]
Issuances				[4]
Transfers out of Level 3				[4]
Ending balance	$ 39.8	[4]	$ 39.8	[4]

[1] There were no OTTI losses recorded in net earnings related to level 3 instruments still held as of September 30, 2012.

[2] Principally consists of Level 3 assets acquired as part of the merger.

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

[4] Includes partnership investments accounted for on an AFS basis.