Supplemental Financial Information (Leases Narrative) (Details) $ in Millions	3 Months Ended
	Mar. 31, 2019 USD ($)
Lessee, Lease, Description [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
NBCUniversal Media LLC [Member]
Lessee, Lease, Description [Line Items]
Operating Lease Expense Inclusive Of Short Term And Variable Lease Expenses	$ 111
Weighted average remaining lease term for operating leases	15 years
Weighted average discount rate used to calculate operating lease liabilities	4.03%
Cash payments for operating leases	$ 64