Reconciliations of Changes in Level Three Assets Measured at Fair Value (Detail) (USD $) In Millions, unless otherwise specified	6 Months Ended
	Jun. 30, 2014		Jun. 30, 2013
Fair Value, Assets Measured on Recurring Basis, Unobservable Input Reconciliation [Line Items]
Beginning balance	$ 708.5		$ 214.3
Net realized/unrealized gains (losses) included in:
Net earnings	1.5	[1]	0.9	[1]
Other comprehensive income	1.8		3.4
Purchases	609.1		109.8
Sales	(62.5)		(24.5)
Issuances
Settlements	(66.1)		(21.0)
Transfers into Level 3	38.1		21.7
Transfers out of Level 3	(238.1)
Ending balance	992.3		304.6
Debt Securities | U.S. corporate bonds
Fair Value, Assets Measured on Recurring Basis, Unobservable Input Reconciliation [Line Items]
Beginning balance	27.5		30.4
Net realized/unrealized gains (losses) included in:
Net earnings	(0.1)	[1]	0.3	[1]
Other comprehensive income	0.1		(0.6)
Purchases	12.0
Sales	(7.7)		(23.8)
Issuances
Settlements	(4.6)		(0.7)
Transfers into Level 3	9.0
Ending balance	36.2		5.6
Debt Securities | Foreign corporate bonds
Fair Value, Assets Measured on Recurring Basis, Unobservable Input Reconciliation [Line Items]
Beginning balance	1.0
Net realized/unrealized gains (losses) included in:
Purchases	1.9
Sales	(1.1)
Issuances
Ending balance	1.8
Debt Securities | Mortgage and asset backed securities | RMBS
Fair Value, Assets Measured on Recurring Basis, Unobservable Input Reconciliation [Line Items]
Beginning balance	78.8		59.6
Net realized/unrealized gains (losses) included in:
Net earnings	2.2	[1]	0.3	[1]
Other comprehensive income	0.8		4.0
Issuances
Settlements	(6.2)		(4.5)
Transfers into Level 3			21.3
Ending balance	75.6		80.7
Debt Securities | Mortgage and asset backed securities | CMBS
Fair Value, Assets Measured on Recurring Basis, Unobservable Input Reconciliation [Line Items]
Beginning balance	60.8		76.1
Net realized/unrealized gains (losses) included in:
Net earnings	(0.2)	[1]	0.1	[1]
Other comprehensive income	0.1		(1.7)
Purchases	14.0		9.8
Sales	(1.0)		(0.7)
Issuances
Settlements	(26.7)		(5.8)
Transfers into Level 3			0.1
Ending balance	47.0		77.9
Debt Securities | Mortgage and asset backed securities | Other asset-backed securities
Fair Value, Assets Measured on Recurring Basis, Unobservable Input Reconciliation [Line Items]
Beginning balance	258.4		5.9
Net realized/unrealized gains (losses) included in:
Net earnings	(0.3)	[1]	0.2	[1]
Other comprehensive income	(0.4)		(0.5)
Purchases	581.2
Sales	(52.7)
Issuances
Settlements	(7.7)		(4.3)
Transfers into Level 3	29.1		0.3
Ending balance	807.6		1.6
Other invested assets
Fair Value, Assets Measured on Recurring Basis, Unobservable Input Reconciliation [Line Items]
Beginning balance	282.0	[2]	42.3	[2]
Net realized/unrealized gains (losses) included in:
Net earnings	(0.1)	[1],[2]
Other comprehensive income	1.2	[2]	2.2	[2]
Purchases			100.0	[2]
Issuances		[2]		[2]
Settlements	(20.9)	[2]	(5.7)	[2]
Transfers out of Level 3	(238.1)	[2]
Ending balance	$ 24.1	[2]	$ 138.8	[2]

[1] There were no other than temporary impairment ("OTTI") losses recorded in net earnings related to Level 3 investments still held as of June 30, 2014 and 2013.

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