Leases (Schedule of Future Minimum Lease Payments for Capital and Operating Leases) (Details) $ in Millions	Dec. 31, 2018 USD ($)
Leases [Abstract]
Operating Leases, Future Minimum Payments Due, Next Twelve Months	$ 188	[1]
Operating Leases, Future Minimum Payments, Due in Two Years	157	[1]
Operating Leases, Future Minimum Payments, Due in Three Years	121	[1]
Operating Leases, Future Minimum Payments, Due in Four Years	98	[1]
Operating Leases, Future Minimum Payments, Due in Five Years	79	[1]
Operating Leases, Future Minimum Payments, Due Thereafter	234	[1]
Operating Leases, Future Minimum Payments Due, Total	877	[1]
Capital Leases, Future Minimum Payments Due, Next Twelve Months	12
Capital Leases, Future Minimum Payments Due in Two Years	10
Capital Leases, Future Minimum Payments Due in Three Years	8
Capital Leases, Future Minimum Payments Due in Four Years	7
Capital Leases, Future Minimum Payments Due in Five Years	14
Capital Leases, Future Minimum Payments Due Thereafter	121
Capital Leases, Total minimum future payments	172
Less: Imputed interest	(80)
Total capital lease obligations	92
Less: Current portion	(8)
Long-term capital lease obligations	84
Financing Obligations Future Minimum Payments Due Current	12
Financing Obligations Future Minimum Payments Due In Two Years	9
Financing Obligations Future Minimum Payments Due In Three Years	10
Financing Obligations Future Minimum Payments Due In Four Years	10
Financing Obligations Future Minimum Payments Due In Five Years	10
Financing Obligations Future Minimum Payments Due Thereafter	106
Financing Obligations, Total minimum future payments	157
Less: Imputed interest	(18)
Total financing obligations	139
Less: Current portion	(5)
Long-term financing obligations	$ 134

[1] Minimum lease payments have not been reduced by minimum sublease rentals due in the future, which are considered immaterial.