Commitments, Contingencies and Other Items - Purchase Commitments (Details) $ in Millions	12 Months Ended
	Dec. 31, 2017 USD ($)
Long-term Purchase Commitment
2018	$ 175
2019	93
2020	67
2021	34
2022	25
Thereafter	70
Total	464
Cost of Access Services
Long-term Purchase Commitment
2018	115
2019	52
2020	35
2021	15
2022	7
Thereafter	2
Total	226
Third-Party Maintenance Services
Long-term Purchase Commitment
2018	60
2019	41
2020	32
2021	19
2022	18
Thereafter	68
Total	$ 238