Assets by Segment (Detail) (USD $) In Millions, unless otherwise specified	Jun. 30, 2014	Dec. 31, 2013
Segment Reporting Information
Assets	$ 62,218.1	$ 59,403.6
Unum US
Segment Reporting Information
Assets	18,731.0	18,384.3
Unum UK
Segment Reporting Information
Assets	3,987.0	3,654.1
Colonial Life
Segment Reporting Information
Assets	3,613.5	3,482.9
Closed Block
Segment Reporting Information
Assets	33,062.6	31,564.2
Corporate and Other
Segment Reporting Information
Assets	$ 2,824.0	$ 2,318.1