Goodwill and Intangibles, including DAC and VOBA - Estimated Amortization Expense for VOBA and DAC in Future Fiscal Periods (Detail) (USD $) In Millions, unless otherwise specified	Mar. 31, 2013
Schedule Of Amortization Expense And Weighted Average Lives Of Identified Intangible Assets [Line Items]
2013	$ 78.5
2014	78.5
2015	78.5
2016	78.5
2017	78.5
VOBA [Member]
Schedule Of Amortization Expense And Weighted Average Lives Of Identified Intangible Assets [Line Items]
2013	20.6
2014	49.7
2015	45.6
2016	41.7
2017	35.1
Thereafter	175.3
DAC [Member]
Schedule Of Amortization Expense And Weighted Average Lives Of Identified Intangible Assets [Line Items]
2013	6.5
2014	17.7
2015	18.6
2016	17.9
2017	16.9
Thereafter	$ 191.1