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Summary of Collateral Covenants and Cross Default Provisions (Parenthetical) (Detail) $ in Billions | 12 Months Ended
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Dec. 31, 2017 USD ($)
Credit Agreement |
Debt Instrument [Line Items] |
Unrestricted liquidity required for credit agreement | $ 2.0
Minimum ratio of appraised value of collateral for Credit Agreement | 160.00%
6.375% Senior Notes due 2018 |
Debt Instrument [Line Items] |
Debt instrument stated interest rate | 6.375%
Debt instrument maturity year | 2018
6% Senior Notes due 2020 |
Debt Instrument [Line Items] |
Debt instrument stated interest rate | 6.00%
Debt instrument maturity year | 2020
5% Senior Notes due 2024 |
Debt Instrument [Line Items] |
Debt instrument stated interest rate | 5.00%
Debt instrument maturity year | 2024
4.25% Senior Notes due 2022 |
Debt Instrument [Line Items] |
Debt instrument stated interest rate | 4.25%
Debt instrument maturity year | 2022

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- Definition Contractual interest rate for funds borrowed, under the debt agreement. + References Reference 1: http://www.xbrl.org/2003/role/presentationRef -Publisher FASB -Name Accounting Standards Codification -Topic 210 -SubTopic 10 -Section S99 -Paragraph 1 -Subparagraph (SX 210.5-02.22(a)(1)) -URI http://asc.fasb.org/extlink&oid=6877327&loc=d3e13212-122682 + Details
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