Debt - Additional Information Domain (Detail) (USD $) In Millions, except Per Share data, unless otherwise specified	12 Months Ended				3 Months Ended	12 Months Ended												12 Months Ended
	Dec. 31, 2013 Integer	Dec. 31, 2012	Dec. 31, 2011	Dec. 31, 2010	Dec. 31, 2013 Northwind Holdings LLC [Member]	Dec. 31, 2013 Northwind Holdings LLC [Member]	Dec. 31, 2012 Northwind Holdings LLC [Member]	Dec. 31, 2011 Northwind Holdings LLC [Member]	Dec. 31, 2007 Northwind Holdings LLC [Member]	Dec. 31, 2013 Tailwind Holdings LLC [Member]	Dec. 31, 2012 Tailwind Holdings LLC [Member]	Dec. 31, 2006 Tailwind Holdings LLC [Member]	Dec. 31, 2013 Notes 5 Point 750 Due 2042 Callable At or Above Par [Member]	Dec. 31, 2012 Notes 5 Point 750 Due 2042 Callable At or Above Par [Member]	Dec. 31, 2013 Notes 6 Point 85 Percent due 2015 callable at or above par [Member]	Dec. 31, 2013 Junior Subordinated Debt Securities 7 Point 405 Percent due 2038 [Member]	Dec. 31, 1998 Junior Subordinated Debt Securities 7 Point 405 Percent due 2038 [Member]	Dec. 31, 2011 Notes 7 Point 625 Percent due 2011 callable at or above par, current portion [Member]	Dec. 31, 2011 Notes 7 Point 625 Percent due 2011 callable at or above par, current portion [Member] Medium-term Notes 7 Point 0 Percent to 7 Point 2 Percent due 2023 to 2028 noncallable [Member]	Dec. 31, 2013 Notes 7 Point 625 Percent due 2011 callable at or above par, current portion [Member] Medium-term Notes 7 Point 0 Percent to 7 Point 2 Percent due 2023 to 2028 noncallable [Member]	Dec. 31, 2013 Receive Fixed/Pay Variable Swap [Member]	Dec. 31, 2012 Receive Fixed/Pay Variable Swap [Member]	Dec. 31, 2011 Receive Fixed/Pay Variable Swap [Member]	Dec. 31, 2010 Receive Fixed/Pay Variable Swap [Member]
Debt Narrative Detail Information [Line Items]
Long-term Debt, Maturities, Repayments of Principal in Year Two	$ 296.9
Long-term Debt, Maturities, Repayments of Principal in Year Three	350.0
Long-term Debt, Maturities, Repayments of Principal in Year Five	200.0
Long-term Debt, Maturities, Repayments of Principal after Year Five	1,772.6
Proceeds from Issuance of Senior Long-term Debt									800.0			130.0
Debt Instrument, Basis Spread on Variable Rate					0.78%
Debt service coverage account (DSCA)					7.4	7.4
Debt Instrument, Periodic Payment, Principal						60.0	60.0	74.4		10.0	10.0
Repayments of Long-term Debt	116.2	70.0	84.4							62.5
Gains (Losses) on Extinguishment of Debt										4.0
Proceeds from Unsecured Notes Payable													250.0	250.0
Repayments of Medium-term Notes																		225.1	225.1
Percentage_ownership_of_Unum_to_PFT																	100.00%
Liquidation value per capital security																$ 1,000	$ 1,000
Debt Instrument, Interest Rate, Stated Percentage															6.85%	7.405%	7.405%	7.625%		7.625%
Derivative, Notional Amount	1,477.4	1,432.8	1,413.0	1,681.9																	600.0	750.0	685.0	890.0
Interest Paid	144.6	139.6	145.4
LineofCreditFacilityTermPeriod	5
Line of Credit Facility, Maximum Borrowing Capacity	400.0
Line Of Credit Facility Maximum Borrowing Capacity If Requested	600.0
Line of Credit Facility, Amount Outstanding	$ 0