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

Reference 1: http://fasb.org/us-gaap/role/ref/legacyRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 835
-SubTopic 30
-Section 45
-Paragraph 2
-URI http://asc.fasb.org/extlink&oid=114775744&loc=d3e28551-108399

Reference 2: http://fasb.org/us-gaap/role/ref/legacyRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 835
-SubTopic 30
-Section 55
-Paragraph 8
-URI http://asc.fasb.org/extlink&oid=114775985&loc=d3e28878-108400

+ Details

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Namespace Prefix:	us-gaap_
Data Type:	xbrli:monetaryItemType
Balance Type:	credit
Period Type:	instant

- Definition

Contractual interest rate for funds borrowed, under the debt 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(a)(1))
-URI http://asc.fasb.org/extlink&oid=6877327&loc=d3e13212-122682

+ Details

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Namespace Prefix:	us-gaap_
Data Type:	num:percentItemType
Balance Type:	na
Period Type:	instant

- 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.

+ Details

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Namespace Prefix:	us-gaap_
Data Type:	xbrli:stringItemType
Balance Type:	na
Period Type:	duration

- Definition

Face (par) amount of the original debt instrument that was repurchased.

+ References

No definition available.

+ Details

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Namespace Prefix:	us-gaap_
Data Type:	xbrli:monetaryItemType
Balance Type:	debit
Period Type:	instant

- Definition

Difference between the fair value of payments made and the carrying amount of debt which is extinguished prior to maturity.

+ References

Reference 1: http://fasb.org/us-gaap/role/ref/legacyRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 470
-SubTopic 50
-Section 40
-Paragraph 4
-URI http://asc.fasb.org/extlink&oid=114001942&loc=d3e12355-112629

Reference 2: http://fasb.org/us-gaap/role/ref/legacyRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 470
-SubTopic 50
-Section 40
-Paragraph 2
-URI http://asc.fasb.org/extlink&oid=114001942&loc=d3e12317-112629

Reference 3: http://fasb.org/us-gaap/role/ref/legacyRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 230
-SubTopic 10
-Section 45
-Paragraph 28
-Subparagraph (b)
-URI http://asc.fasb.org/extlink&oid=109223946&loc=d3e3602-108585

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Namespace Prefix:	us-gaap_
Data Type:	xbrli:monetaryItemType
Balance Type:	credit
Period Type:	duration

- 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.

+ 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

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Namespace Prefix:	us-gaap_
Data Type:	xbrli:monetaryItemType
Balance Type:	credit
Period Type:	instant

Indebtedness (Activity) (Details)	1 Months Ended	12 Months Ended
Indebtedness (Activity) (Details)	Nov. 30, 2016 USD ($)	Dec. 31, 2018 USD ($)	Dec. 31, 2017 USD ($)	Dec. 31, 2016 USD ($)	Jan. 31, 2019 USD ($)	Dec. 31, 2018 GBP (£)	Oct. 31, 2017 USD ($)	Oct. 30, 2017 USD ($)	Sep. 30, 2016 USD ($)
Debt Instrument [Line Items]
Debt instrument, face amount		$ 3,105,626,000
Loss on debt extinguishment		0	$ 49,000	$ 27,099,000
Senior Notes \| 3.25% Senior Notes
Debt Instrument [Line Items]
Debt instrument, face amount									$ 400,000,000
Stated interest rate									3.25%
Senior Notes \| 5.5% Senior Note
Debt Instrument [Line Items]
Stated interest rate									5.50%
Repurchased face amount of debt									$ 300,000,000
Senior Notes \| 6.625% Senior Note
Debt Instrument [Line Items]
Stated interest rate	6.625%
Repurchased face amount of debt	$ 296,500,000.0
Unsecured Debt
Debt Instrument [Line Items]
Debt instrument, face amount		$ 2,300,000,000
Medium-term Notes \| 7.5% Medium Term Note
Debt Instrument [Line Items]
Stated interest rate	7.50%
Repurchased face amount of debt	$ 100,000,000.0
Mortgages \| Mortgage Loan, 2.64%
Debt Instrument [Line Items]
Debt instrument, face amount \| £						£ 129,500,000.0
Stated interest rate		2.64%				2.64%
Unsecured Debt
Debt Instrument [Line Items]
Loss on debt extinguishment	$ 27,100,000
Revolving Credit Facility \| Credit Facility Group Lenders
Debt Instrument [Line Items]
Maximum borrowing capacity		$ 800,000,000
Revolving Credit Facility \| Credit Facility Group Lenders \| 2014 Credit Facility
Debt Instrument [Line Items]
Maximum borrowing capacity								$ 800,000,000
Revolving Credit Facility \| Credit Facility Group Lenders \| 2017 Credit Facility
Debt Instrument [Line Items]
Maximum borrowing capacity								800,000,000
Commercial Paper \| Credit Facility Group Lenders
Debt Instrument [Line Items]
Maximum borrowing capacity		$ 100,000,000
Commercial Paper \| Credit Facility Group Lenders \| 2017 Credit Facility
Debt Instrument [Line Items]
Maximum borrowing capacity								100,000,000
Credit Facilities \| Working Capital Facility Lender
Debt Instrument [Line Items]
Maximum borrowing capacity							$ 30,000,000
Credit Facilities \| Working Capital Facility Lender \| 2017 Credit Facility
Debt Instrument [Line Items]
Maximum borrowing capacity								$ 30,000,000
Subsequent Event \| Senior Notes \| 4.375% Senior Unsecured Notes
Debt Instrument [Line Items]
Debt instrument, face amount					$ 350,000,000
Stated interest rate					4.375%