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Credit and Other Debt Agreements - Credit Agreement - Additional Information (Detail) $ in Millions |  | 12 Months Ended |
--- | --- | --- | ---
Apr. 08, 2016 USD ($) Institution | Dec. 31, 2018 USD ($) | Dec. 31, 2018 NZD ($) | Dec. 31, 2018 AUD ($) | Dec. 31, 2017 USD ($) | [1] | Dec. 31, 2016 USD ($) | [1] | Dec. 31, 2018 NZD ($) | Dec. 31, 2018 AUD ($)
Debt Instrument [Line Items] |  |  |  |  |  |  |  |
Liabilities |  | $ 11,764,300,000 |  |  | $ 10,610,000,000 |  |  |
Line of credit facility, increase in additional borrowings |  | 3,075,000,000 |  |  | $ 3,643,000,000 | $ 2,740,000,000 |  |
Long-term debt |  | $ 19,900,000 |  |  |  |  |  |
Revolving Credit Facility [Member] |  |  |  |  |  |  |  |
Debt Instrument [Line Items] |  |  |  |  |  |  |  |
Date of expire |  | May 18, 2020 | May 18, 2020 | May 18, 2020 |  |  |  |
Interest rate for facility |  | The interest rates on Facility B are Interbank rates, which vary by tranche, duration and currency, plus a margin of 1.05%. The interest rates on Facilities C and D are 30 day Interbank rates, plus a margin of 0.55%. The annual fee for Facility B is 0.4725% of the undrawn commitments for the two tranches of the facility. The annual fee for Facilities C and D is 0.50% of the total commitments of the facilities. | The interest rates on Facility B are Interbank rates, which vary by tranche, duration and currency, plus a margin of 1.05%. The interest rates on Facilities C and D are 30 day Interbank rates, plus a margin of 0.55%. The annual fee for Facility B is 0.4725% of the undrawn commitments for the two tranches of the facility. The annual fee for Facilities C and D is 0.50% of the total commitments of the facilities. | The interest rates on Facility B are Interbank rates, which vary by tranche, duration and currency, plus a margin of 1.05%. The interest rates on Facilities C and D are 30 day Interbank rates, plus a margin of 0.55%. The annual fee for Facility B is 0.4725% of the undrawn commitments for the two tranches of the facility. The annual fee for Facilities C and D is 0.50% of the total commitments of the facilities. |  |  |  |
Debt instrument fair value amount |  | $ 154,000,000 |  |  |  |  |  |
Credit Facility Two [Member] | Revolving Credit Facility [Member] |  |  |  |  |  |  |  |
Debt Instrument [Line Items] |  |  |  |  |  |  |  |
Line of credit facility, amount outstanding |  |  |  |  |  |  | $ 15.0 | $ 190,000,000
Line of credit facility, remaining borrowing capacity |  |  |  |  |  |  | 10.0 | 0
Net borrowings on premium financing debt facility |  |  | $ 25.0 | $ 160,000,000 |  |  |  |
Additional margin percentage on interest rate |  | 1.05% | 1.05% | 1.05% |  |  |  |
Annual fee percentage |  | 0.4725% | 0.4725% | 0.4725% |  |  |  |
Credit Facility Two [Member] | Revolving Credit Facility [Member] | Minimum [Member] |  |  |  |  |  |  |  |
Debt Instrument [Line Items] |  |  |  |  |  |  |  |
Increase in premium financing debt facility |  |  |  | $ 160,000,000 |  |  |  |
Credit Facility Three [Member] | Revolving Credit Facility [Member] |  |  |  |  |  |  |  |
Debt Instrument [Line Items] |  |  |  |  |  |  |  |
Line of credit facility, amount outstanding |  |  |  |  |  |  |  | 0
Line of credit facility, remaining borrowing capacity |  |  |  |  |  |  | 0.1 | 25,000,000
Net borrowings on premium financing debt facility |  |  |  | $ 25,000,000 |  |  |  |
Additional margin percentage on interest rate |  | 0.55% | 0.55% | 0.55% |  |  |  |
Annual fee percentage |  | 0.50% | 0.50% | 0.50% |  |  |  |
Credit Facility Four [Member] | Revolving Credit Facility [Member] |  |  |  |  |  |  |  |
Debt Instrument [Line Items] |  |  |  |  |  |  |  |
Line of credit facility, amount outstanding |  |  |  |  |  |  | 14.9 |
Line of credit facility, remaining borrowing capacity |  |  |  |  |  |  | $ 0.1 | $ 25,000,000
Net borrowings on premium financing debt facility |  |  | $ 15.0 |  |  |  |  |
Additional margin percentage on interest rate |  | 0.55% | 0.55% | 0.55% |  |  |  |
Annual fee percentage |  | 0.50% | 0.50% | 0.50% |  |  |  |
Multi Currency Credit Agreement [Member] |  |  |  |  |  |  |  |
Debt Instrument [Line Items] |  |  |  |  |  |  |  |
Number of financial institutions entered in unsecured multicurrency credit agreement | Institution | 15 |  |  |  |  |  |  |
Line of credit facility, maximum amount outstanding during period |  | $ 1,100,000,000 |  |  |  |  |  |
Debt acquisition costs |  | 2,000,000 |  |  |  |  |  |
Estimated fair value of outstanding borrowings |  | $ 265,000,000 |  |  |  |  |  |
Multi Currency Credit Agreement [Member] | Minimum [Member] |  |  |  |  |  |  |  |
Debt Instrument [Line Items] |  |  |  |  |  |  |  |
Debt instrument, maturity date | Sep. 19, 2018 |  |  |  |  |  |  |
Line of credit facility, maximum borrowing capacity | $ 600,000,000 |  |  |  |  |  |  |
Interest rates on base rate loans |  | 0.00% | 0.00% | 0.00% |  |  |  |
Fixed rate over LIBOR |  | 0.85% | 0.85% | 0.85% |  |  |  |
Annual facility fee of revolving credit facility |  | 0.15% | 0.15% | 0.15% |  |  |  |
Multi Currency Credit Agreement [Member] | Maximum [Member] |  |  |  |  |  |  |  |
Debt Instrument [Line Items] |  |  |  |  |  |  |  |
Debt instrument, maturity date | Apr. 08, 2021 |  |  |  |  |  |  |
Line of credit facility, maximum borrowing capacity | $ 800,000,000 |  |  |  |  |  |  |
Interest rates on base rate loans |  | 0.45% | 0.45% | 0.45% |  |  |  |
Fixed rate over LIBOR |  | 1.45% | 1.45% | 1.45% |  |  |  |
Annual facility fee of revolving credit facility |  | 0.30% | 0.30% | 0.30% |  |  |  |
Multi Currency Credit Agreement [Member] | Swing Loan [Member] |  |  |  |  |  |  |  |
Debt Instrument [Line Items] |  |  |  |  |  |  |  |
Long-term debt, gross |  | $ 75,000,000 |  |  |  |  |  |
Multi Currency Credit Agreement [Member] | Standby Letters of Credit [Member] |  |  |  |  |  |  |  |
Debt Instrument [Line Items] |  |  |  |  |  |  |  |
Long-term debt, gross |  | 75,000,000 |  |  |  |  |  |
Line of credit facility, amount outstanding |  | 17,000,000 |  |  |  |  |  |
Liabilities |  | 15,800,000 |  |  |  |  |  |
Line of credit facility, fair value of amount outstanding |  | 265,000,000 |  |  |  |  |  |
Line of credit facility, remaining borrowing capacity |  | 518,000,000 |  |  |  |  |  |
Line of credit facility, increase in additional borrowings |  | 58,000,000 |  |  |  |  |  |
Note Purchase Agreements [Member] | Level 3 [Member] |  |  |  |  |  |  |  |
Debt Instrument [Line Items] |  |  |  |  |  |  |  |
Line of credit facility, fair value of amount outstanding |  | 3,194,400,000 |  |  |  |  |  |
Long-term debt |  | $ 3,198,000,000 |  |  |  |  |  |
Line Of Credit Facility Five [Member] | Revolving Credit Facility [Member] |  |  |  |  |  |  |  |
Debt Instrument [Line Items] |  |  |  |  |  |  |  |
Date of expire |  | Jan. 31, 2019 | Jan. 31, 2019 | Jan. 31, 2019 |  |  |  |
Line Of Credit Facility Five [Member] | Revolving Credit Facility [Member] | Maximum [Member] |  |  |  |  |  |  |  |
Debt Instrument [Line Items] |  |  |  |  |  |  |  |
Increase in premium financing debt facility |  |  |  | $ 190,000,000 |  |  |  |
[1] | See Note 3 - Revenues from Contracts with Customers for additional information about the restatements related to Topic 606.

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- Definition Amount, before unamortized (discount) premium and debt issuance costs, of long-term debt. Includes, but is not limited to, notes payable, bonds payable, commercial loans, mortgage loans, convertible debt, subordinated debt and other types of debt. + References Reference 1: http://www.xbrl.org/2003/role/disclosureRef -Publisher FASB -Name Accounting Standards Codification -Topic 470 -SubTopic 20 -Section 50 -Paragraph 4 -Subparagraph (b)(1) -URI http://asc.fasb.org/extlink&oid=109500613&loc=SL6031897-161870 Reference 2: http://fasb.org/us-gaap/role/ref/legacyRef -Publisher FASB -Name Accounting Standards Codification -Topic 944 -SubTopic 210 -Section S99 -Paragraph 1 -Subparagraph (SX 210.7-03(16)) -URI http://asc.fasb.org/extlink&oid=6879938&loc=d3e572229-122910 Reference 3: http://fasb.org/us-gaap/role/ref/legacyRef -Publisher FASB -Name Accounting Standards Codification -Topic 210 -SubTopic 10 -Section S99 -Paragraph 1 -Subparagraph (SX 210.5-02(22)) -URI http://asc.fasb.org/extlink&oid=6877327&loc=d3e13212-122682 Reference 4: http://fasb.org/us-gaap/role/ref/legacyRef -Publisher FASB -Name Accounting Standards Codification -Topic 942 -SubTopic 210 -Section S99 -Paragraph 1 -Subparagraph (SX 210.9-03(16)) -URI http://asc.fasb.org/extlink&oid=6876686&loc=d3e534808-122878 + Details
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- Definition The carrying value as of the balance sheet date of the current and noncurrent portions of long-term obligations drawn from a line of credit, which is a bank's commitment to make loans up to a specific amount. Examples of items that might be included in the application of this element may consist of letters of credit, standby letters of credit, and revolving credit arrangements, under which borrowings can be made up to a maximum amount as of any point in time conditional on satisfaction of specified terms before, as of and after the date of drawdowns on the line. Includes short-term obligations that would normally be classified as current liabilities but for which (a) postbalance sheet date issuance of a long term obligation to refinance the short term obligation on a long term basis, or (b) the enterprise has entered into a financing agreement that clearly permits the enterprise to refinance the short-term obligation on a long term basis and the following conditions are met (1) the agreement does not expire within 1 year and is not cancelable by the lender except for violation of an objectively determinable provision, (2) no violation exists at the BS date, and (3) the lender has entered into the financing agreement is expected to be financially capable of honoring the agreement. + References Reference 1: http://fasb.org/us-gaap/role/ref/legacyRef -Publisher FASB -Name Accounting Standards Codification -Topic 210 -SubTopic 10 -Section S99 -Paragraph 1 -Subparagraph (SX 210.5-02(22)) -URI http://asc.fasb.org/extlink&oid=6877327&loc=d3e13212-122682 Reference 2: http://fasb.org/us-gaap/role/ref/legacyRef -Publisher FASB -Name Accounting Standards Codification -Topic 942 -SubTopic 210 -Section S99 -Paragraph 1 -Subparagraph (SX 210.9-03(16)) -URI http://asc.fasb.org/extlink&oid=6876686&loc=d3e534808-122878 Reference 3: http://fasb.org/us-gaap/role/ref/legacyRef -Publisher FASB -Name Accounting Standards Codification -Topic 944 -SubTopic 210 -Section S99 -Paragraph 1 -Subparagraph (SX 210.7-03(16)) -URI http://asc.fasb.org/extlink&oid=6879938&loc=d3e572229-122910 + Details
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- Definition The fee, expressed as a percentage of the line of credit facility, for the line of credit facility regardless of whether the facility has been used. + References No definition available. + Details
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- Definition Description of the interest rate for the amounts borrowed under the credit facility, including the terms and the method for determining the interest rate (for example, fixed or variable, LIBOR plus a percentage, increasing rate, timing of interest rate resets, remarketing provisions). + References Reference 1: http://fasb.org/us-gaap/role/ref/legacyRef -Publisher FASB -Name Accounting Standards Codification -Topic 210 -SubTopic 10 -Section S99 -Paragraph 1 -Subparagraph (SX 210.5-02.19(b),22(b)) -URI http://asc.fasb.org/extlink&oid=6877327&loc=d3e13212-122682 + Details
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