Percentage points added to the reference rate to compute the variable rate on the debt instrument.

No definition available.

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- Definition

Face (par) amount of debt instrument at time of issuance.

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- Definition

Contractual interest rate for funds borrowed, under the debt agreement.

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- Definition

Line items represent financial concepts included in a table. These concepts are used to disclose reportable information associated with domain members defined in one or many axes to the table.

+ References

No definition available.

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- Definition

Period of time between issuance and maturity of debt instrument, in PnYnMnDTnHnMnS' format, for example, 'P1Y5M13D' represents the reported fact of one year, five months, and thirteen days.

+ References

No definition available.

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- Definition

The cash outflow from the repayment of long-term borrowing where a lender is placed in a lien position behind debt having a higher priority of repayment (senior) in case of liquidation of the entity's assets before its maturity.

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- Definition

Maximum borrowing capacity under the credit facility without consideration of any current restrictions on the amount that could be borrowed or the amounts currently outstanding under the facility.

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- Definition

The cash inflow from additional borrowings, net of cash paid to third parties in connection with debt origination.

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- Definition

Amount of cash inflow from contractual arrangement with the lender, including but not limited to, letter of credit, standby letter of credit and revolving credit arrangements.

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The cash outflow during the period from the repayment of aggregate short-term and long-term debt. Excludes payment of capital lease obligations.

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Amount of unrealized gain (loss) related to the increase or decrease in fair value of interest rate derivatives designated as cash flow hedging instruments, which was recorded in accumulated other comprehensive income to the extent that the cash flow hedge was determined to be effective.

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Debt - Additional Information (Detail) - USD ($)		1 Months Ended		3 Months Ended		6 Months Ended		12 Months Ended
Debt - Additional Information (Detail) - USD ($)	Apr. 03, 2017	Mar. 31, 2018	Apr. 30, 2017	Mar. 31, 2018	Sep. 30, 2017	Jun. 30, 2018	Jun. 30, 2017	Dec. 31, 2017
Debt Instrument [Line Items]
Repayments of Debt						$ 37,100,000	$ 12,500,000
Repayment of debt						0	$ 594,400,000
Discretionary Line of Credit
Debt Instrument [Line Items]
Maximum borrowing capacity						$ 250,000,000
Debt term						30 days
Borrowings outstanding						$ 0		$ 0
3.75% Senior Notes due 2021
Debt Instrument [Line Items]
Debt, stated interest rate						3.75%
2.45% Senior Notes due 2027
Debt Instrument [Line Items]
Debt, stated interest rate						2.45%
6 5/8% Senior Notes due 2029
Debt Instrument [Line Items]
Debt, stated interest rate						6.625%
6.25% Senior Notes due 2032
Debt Instrument [Line Items]
Debt, stated interest rate						6.25%
4.35% Senior Notes due 2044
Debt Instrument [Line Items]
Debt, stated interest rate						4.35%
3.70% Senior Notes due 2045
Debt Instrument [Line Items]
Debt, stated interest rate						3.70%
4.125% Senior Notes due 2047
Debt Instrument [Line Items]
Debt, face amount	$ 850,000,000		$ 850,000,000
Debt, stated interest rate	4.125%		4.125%			4.125%
Proceeds, net of underwriter's discounts and commissions			$ 841,100,000
Unrealized gain (loss) on interest rate cash flow hedges	$ (8,000,000)		$ (8,000,000)
4.20% Senior Notes due 2048
Debt Instrument [Line Items]
Debt, face amount		$ 600,000,000		$ 600,000,000
Debt, stated interest rate		4.20%		4.20%		4.20%
Proceeds, net of underwriter's discounts and commissions		$ 589,500,000
Federal Funds Open Rate \| Discretionary Line of Credit
Debt Instrument [Line Items]
Debt Instrument, Basis Spread on Variable Rate						0.50%
Notes Payable, Other Payables \| Other debt instruments
Debt Instrument [Line Items]
Repayments of Debt				$ 37,100,000
Trust Preferred Debt Securities [Member] \| Other debt instruments
Debt Instrument [Line Items]
Repayments of Debt					$ 65,200,000