Fair Value Measurements (Estimated Fair Values of Long-Term Debt) (Details) $ in Millions	9 Months Ended
Sep. 30, 2016 USD ($)
$750.0 million fixed rate notes due September 2022, stated rate of 3.00% [Member]
Debt Instrument, Face Amount	$ 750.0
Debt Instrument, Maturity Date	Sep. 01, 2022
Debt Instrument, Interest Rate, Stated Percentage	3.00%
$750.0 million fixed rate notes due March 2025, stated rate of 3.00% [Member]
Debt Instrument, Face Amount	$ 750.0
Debt Instrument, Maturity Date	Mar. 01, 2025
Debt Instrument, Interest Rate, Stated Percentage	3.00%
$750.0 million fixed rate notes due September 2043, stated rate of 5.30% [Member]
Debt Instrument, Face Amount	$ 750.0
Debt Instrument, Maturity Date	Sep. 01, 2043
Debt Instrument, Interest Rate, Stated Percentage	5.30%
Fair Value, Inputs, Level 2 [Member] \| $750.0 million fixed rate notes due September 2022, stated rate of 3.00% [Member]
Debt Instrument, Fair Value Disclosure	$ 798.8
Fair Value, Inputs, Level 2 [Member] \| $750.0 million fixed rate notes due March 2025, stated rate of 3.00% [Member]
Debt Instrument, Fair Value Disclosure	789.8
Fair Value, Inputs, Level 2 [Member] \| $750.0 million fixed rate notes due September 2043, stated rate of 5.30% [Member]
Debt Instrument, Fair Value Disclosure	$ 971.5

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

Reference 1: http://www.xbrl.org/2003/role/presentationRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 835
-SubTopic 30
-Section 55
-Paragraph 8
-URI http://asc.fasb.org/extlink&oid=34725769&loc=d3e28878-108400

Reference 2: http://www.xbrl.org/2003/role/presentationRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 835
-SubTopic 30
-Section 45
-Paragraph 2
-URI http://asc.fasb.org/extlink&oid=6451184&loc=d3e28551-108399

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Fair value portion of debt instrument payable, including, but not limited to, notes payable and loans payable.

+ References

Reference 1: http://www.xbrl.org/2003/role/presentationRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 825
-SubTopic 10
-Section 50
-Paragraph 10
-Subparagraph (a)
-URI http://asc.fasb.org/extlink&oid=49121117&loc=d3e13433-108611

Reference 2: http://www.xbrl.org/2003/role/presentationRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 825
-SubTopic 10
-Section 50
-Paragraph 12
-URI http://asc.fasb.org/extlink&oid=49121117&loc=d3e13476-108611

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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

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- Definition

Date when the debt instrument is scheduled to be fully repaid, in CCYY-MM-DD format.

+ 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)(2))
-URI http://asc.fasb.org/extlink&oid=6877327&loc=d3e13212-122682

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