Transfers of Assets between Level 1 and Level 2 (Detail) (USD $) In Millions, unless otherwise specified	Jun. 30, 2014	Jun. 30, 2013
Second Quarter
Transfers Between Level 1 and Level 2
Level 2 from Level 1 Transfers	$ 2,156.6	$ 1,346.4
Level 1 from Level 2 Transfers	2,926.4	3,627.5
Second Quarter | United States Government and Government Agencies and Authorities
Transfers Between Level 1 and Level 2
Level 2 from Level 1 Transfers	166.0	61.4
Level 1 from Level 2 Transfers	93.3	0
Second Quarter | Public Utilities
Transfers Between Level 1 and Level 2
Level 2 from Level 1 Transfers	265.9	192.5
Level 1 from Level 2 Transfers	275.4	378.6
Second Quarter | All Other Corporate Bonds
Transfers Between Level 1 and Level 2
Level 2 from Level 1 Transfers	1,724.7	1,092.5
Level 1 from Level 2 Transfers	2,557.7	3,248.9
First and Second Quarters
Transfers Between Level 1 and Level 2
Level 2 from Level 1 Transfers	848.3	824.8
Level 1 from Level 2 Transfers	3,649.9	5,116.3
First and Second Quarters | United States Government and Government Agencies and Authorities
Transfers Between Level 1 and Level 2
Level 2 from Level 1 Transfers	0	0
Level 1 from Level 2 Transfers	0	194.1
First and Second Quarters | States, Municipalities, and Political Subdivisions
Transfers Between Level 1 and Level 2
Level 2 from Level 1 Transfers	0	19.4
Level 1 from Level 2 Transfers	0	0
First and Second Quarters | Public Utilities
Transfers Between Level 1 and Level 2
Level 2 from Level 1 Transfers	81.1	33.5
Level 1 from Level 2 Transfers	288.7	550.2
First and Second Quarters | All Other Corporate Bonds
Transfers Between Level 1 and Level 2
Level 2 from Level 1 Transfers	767.2	771.9
Level 1 from Level 2 Transfers	$ 3,361.2	$ 4,372.0