Credit and Other Debt Agreements - Summary of Corporate and Other Debt (Detail) (USD $) In Millions, unless otherwise specified	Dec. 31, 2014	Dec. 31, 2013
Debt Instrument [Line Items]
Semi-annual payments of interest	$ 2,392.9	$ 1,455.5
Premium Financing Debt Facility [Member]
Debt Instrument [Line Items]
Semi-annual payments of interest	127.9
Note Purchase Agreements [Member]
Debt Instrument [Line Items]
Semi-annual payments of interest	2,125.0	925.0
Fixed Rate of 6.26%, Balloon Due 2014 [Member] | Note Purchase Agreements [Member]
Debt Instrument [Line Items]
Semi-annual payments of interest		100.0
Fixed Rate of 6.44%, Balloon Due 2017 [Member] | Note Purchase Agreements [Member]
Debt Instrument [Line Items]
Semi-annual payments of interest	300.0	300.0
Fixed Rate of 2.80%, Balloon Due 2018 [Member] | Note Purchase Agreements [Member]
Debt Instrument [Line Items]
Semi-annual payments of interest	50.0
Fixed Rate of 3.20%, Balloon Due 2019 [Member] | Note Purchase Agreements [Member]
Debt Instrument [Line Items]
Semi-annual payments of interest	50.0
Fixed Rate of 5.85%, $50.0 Million Due in 2016, 2018 and 2019 [Member] | Note Purchase Agreements [Member]
Debt Instrument [Line Items]
Semi-annual payments of interest	150.0	150.0
Fixed Rate of 3.99%, Balloon Due 2020 [Member] | Note Purchase Agreements [Member]
Debt Instrument [Line Items]
Semi-annual payments of interest	50.0	50.0
Fixed Rate of 3.48%, Balloon Due 2020 [Member] | Note Purchase Agreements [Member]
Debt Instrument [Line Items]
Semi-annual payments of interest	50.0
Fixed Rate of 5.18%, Balloon Due 2021 [Member] | Note Purchase Agreements [Member]
Debt Instrument [Line Items]
Semi-annual payments of interest	75.0	75.0
Fixed rate of 3.69%, Balloon Due 2022 [Member] | Note Purchase Agreements [Member]
Debt Instrument [Line Items]
Semi-annual payments of interest	200.0	200.0
Fixed Rate of 5.49%, Balloon Due 2023 [Member] | Note Purchase Agreements [Member]
Debt Instrument [Line Items]
Semi-annual payments of interest	50.0	50.0
Fixed Rate of 4.13%, Balloon Due 2023 [Member] | Note Purchase Agreements [Member]
Debt Instrument [Line Items]
Semi-annual payments of interest	200.0
Fixed Rate of 4.58% Balloon Due 2024 [Member] | Note Purchase Agreements [Member]
Debt Instrument [Line Items]
Semi-annual payments of interest	325.0
Fixed Rate of 4.31%, Balloon Due 2025 [Member] | Note Purchase Agreements [Member]
Debt Instrument [Line Items]
Semi-annual payments of interest	200.0
Fixed Rate of 4.73% Balloon Due 2026 [Member] | Note Purchase Agreements [Member]
Debt Instrument [Line Items]
Semi-annual payments of interest	175.0
Fixed Rate of 4.36%, Balloon Due 2026 [Member] | Note Purchase Agreements [Member]
Debt Instrument [Line Items]
Semi-annual payments of interest	150.0
Fixed Rate of 4.98% Balloon Due 2029 [Member] | Note Purchase Agreements [Member]
Debt Instrument [Line Items]
Semi-annual payments of interest	100.0
Prime or LIBOR plus up to 1.45%, expires September 19, 2018 [Member] | Multi Currency Credit Agreement [Member]
Debt Instrument [Line Items]
Semi-annual payments of interest	140.0	530.5
Interbank rates plus 1.65%, Expires June 15, 2016 [Member] | AUD denominated tranche [Member] | Facility B [Member] | Premium Financing Debt Facility [Member]
Debt Instrument [Line Items]
Semi-annual payments of interest	95.0
Interbank rates plus 1.65%, Expires June 15, 2016 [Member] | NZD denominated tranche [Member] | Facility B [Member] | Premium Financing Debt Facility [Member]
Debt Instrument [Line Items]
Semi-annual payments of interest	17.8
Interbank rates plus 0.85%, Expires June 15, 2016 [Member] | AUD denominated tranche [Member] | Facility C and D [Member] | Premium Financing Debt Facility [Member]
Debt Instrument [Line Items]
Semi-annual payments of interest	7.7
Interbank rates plus 0.85%, Expires June 15, 2016 [Member] | NZD denominated tranche [Member] | Facility C and D [Member] | Premium Financing Debt Facility [Member]
Debt Instrument [Line Items]
Semi-annual payments of interest	$ 7.4