Reconciliations of Changes in Level Three Assets Measured at Fair Value (Detail) (USD $) In Millions, unless otherwise specified	3 Months Ended
	Mar. 31, 2015		Mar. 31, 2014
Fair Value, Assets Measured on Recurring Basis, Unobservable Input Reconciliation [Line Items]
Beginning balance	$ 1,041.4		$ 708.5
Net realized/unrealized gains (losses) included in:
Net earnings	0.7	[1]	1.0	[1]
Other comprehensive income	8.1		0.7
Purchases	42.6		358.8
Sales	(53.8)		(9.9)
Issuances	0		0
Settlements	(5.7)		(26.0)
Transfers into Level 3	0		35.0
Transfers out of Level 3	(10.4)		(5.2)
Ending balance	1,022.9		1,062.9
Debt Securities | U.S. corporate bonds
Fair Value, Assets Measured on Recurring Basis, Unobservable Input Reconciliation [Line Items]
Beginning balance	36.7		27.5
Net realized/unrealized gains (losses) included in:
Net earnings	0.1	[1]
Other comprehensive income	0.4		0.1
Purchases	6.7		8.1
Sales	(0.5)		(7.6)
Issuances	0		0
Settlements	(4.0)		0.8
Transfers into Level 3			5.9
Transfers out of Level 3	(6.8)
Ending balance	32.6		34.8
Debt Securities | Foreign corporate bonds
Fair Value, Assets Measured on Recurring Basis, Unobservable Input Reconciliation [Line Items]
Beginning balance	6.0		1.0
Net realized/unrealized gains (losses) included in:
Purchases			1.3
Sales	(0.2)		(1.1)
Issuances	0		0
Transfers out of Level 3	(3.6)
Ending balance	2.2		1.2
Debt Securities | Mortgage and asset backed securities | RMBS
Fair Value, Assets Measured on Recurring Basis, Unobservable Input Reconciliation [Line Items]
Beginning balance	18.2		78.8
Net realized/unrealized gains (losses) included in:
Net earnings	0.1	[1]	1.0	[1]
Other comprehensive income			0.3
Issuances	0		0
Settlements	(0.7)		(2.2)
Ending balance	17.6		77.9
Debt Securities | Mortgage and asset backed securities | CMBS
Fair Value, Assets Measured on Recurring Basis, Unobservable Input Reconciliation [Line Items]
Beginning balance	23.3		60.8
Net realized/unrealized gains (losses) included in:
Net earnings	(0.1)	[1]	(0.1)	[1]
Other comprehensive income	(0.4)		(0.6)
Purchases	0.9		14.0
Sales			(1.0)
Issuances	0		0
Settlements	(0.5)		(12.5)
Ending balance	23.2		60.6
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	933.1		258.4
Net realized/unrealized gains (losses) included in:
Net earnings	0.6	[1]	0.2	[1]
Other comprehensive income	7.8		0.6
Purchases	35.0		335.4
Sales	(53.1)		(0.2)
Issuances	0		0
Settlements	(0.5)		(2.3)
Transfers into Level 3			29.1
Ending balance	922.9		621.2
Other invested assets
Fair Value, Assets Measured on Recurring Basis, Unobservable Input Reconciliation [Line Items]
Beginning balance	24.1	[2]	282.0	[2]
Net realized/unrealized gains (losses) included in:
Net earnings			(0.1)	[1],[2]
Other comprehensive income	0.3	[2]	0.3	[2]
Issuances	0	[2]	0	[2]
Settlements			(9.8)	[2]
Transfers out of Level 3			(5.2)	[2]
Ending balance	$ 24.4	[2]	$ 267.2	[2]

[1] There were no other than temporary impairment ("OTTI") losses recorded in net earnings related to Level 3 investments still held as of March 31, 2015 and 2014.

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