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Investments (Other Investments) (Details) $ in Billions	Jun. 30, 2018 USD ($) preferred_stock_series	Dec. 31, 2017 USD ($)
Level 2 [Member] | AirTouch [Member]
Schedule of Other Investments [Line Items]
Fair value of redeemable preferred shares	$ 1.7
AirTouch [Member]
Schedule of Other Investments [Line Items]
Number of series of preferred stock | preferred_stock_series	2
Held to maturity investment	$ 1.6	$ 1.6
AirTouch [Member] | Level 2 [Member]
Schedule of Other Investments [Line Items]
Fair value of held to maturity investment redeemable preferred shares	$ 1.7

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- Definition

Fair value of our redeemable subsidiary preferred shares and/or stock

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- Definition

Number of Preferred Stock Series

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- Definition

Fair value of investment in debt security measured at amortized cost (held-to-maturity).

+ References

Reference 1: http://fasb.org/us-gaap/role/ref/legacyRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 320
-SubTopic 10
-Section 50
-Paragraph 5
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- Definition

Amount of investment in debt security measured at amortized cost (held-to-maturity), classified as noncurrent.

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-Publisher FASB
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-Topic 320
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