Commitments and Contingencies (Narrative) (Details) - USD ($) $ in Millions	3 Months Ended
	Mar. 31, 2019	Mar. 31, 2018	Dec. 31, 2018
Commitment And Contingencies [Line Items]
Operating Lease Expense Inclusive Of Short Term And Variable Lease Expenses	$ 274
Weighted average remaining lease term for operating leases	10 years
Weighted average discount rate used to calculate operating lease liabilities	3.84%
Cash payments for operating leases	$ 213
Operating lease expense		$ 186
Redeemable Subsidiary Preferred Stock [Member] | Level 2 [Member]
Commitment And Contingencies [Line Items]
Temporary equity, fair value of redeemable subsidiary preferred stock	$ 739
Sky Limited [Member]
Commitment And Contingencies [Line Items]
Future cash payments related to additional contracts determined to be operating leases			$ 804