Funding Sources (Details) - USD ($) $ in Millions	1 Months Ended	3 Months Ended	9 Months Ended
	Apr. 30, 2016	Mar. 31, 2016	Dec. 31, 2016	Dec. 31, 2015	May 31, 2016
Financing Receivable, Recorded Investment [Line Items]
Sale Leaseback Transaction, Net Book Value		$ 1,200	$ 447	$ 1,300
Sale Leaseback Transaction, Net Proceeds, Investing Activities			0	$ 1,136
Sale Leaseback Transaction, Net Proceeds, Financing Activities		$ 600
MLS 2nd Tranche [Member]
Financing Receivable, Recorded Investment [Line Items]
Sale Leaseback Transaction, Net Book Value			554		$ 1,300
Sale Leaseback Transaction, Net Proceeds, Investing Activities	$ 1,100
Network Sale-Leaseback [Member]
Financing Receivable, Recorded Investment [Line Items]
Sale Leaseback Transaction, Net Book Value	3,000		$ 2,500
Sale Leaseback Transaction, Net Proceeds, Financing Activities	$ 2,200