Fair Value Measurements (Details Textual) - USD ($) $ in Billions	9 Months Ended
	Sep. 30, 2017	Dec. 31, 2016
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Cash and cash equivalents	$ 6.6	$ 7.0
Restricted cash	1.3	1.4
Level 1 | Corporate Bonds
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Fair value of debt	25.0
Level 2 | Other Long-term Investments
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Fair value of debt	0.7
Carrying Value
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Long-term debt, net carrying value	25.0	26.2
Fair Value
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Long-term debt, net carrying value	$ 25.7	$ 26.6
Maximum
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Maturity period of primarily bank time deposits, maximum, classified as cash equivalents and money market funds (in days)	90 days