Leases (Details) - USD ($) $ in Millions	3 Months Ended	9 Months Ended
	Sep. 30, 2019	Sep. 30, 2019	Dec. 31, 2018
Leases [Abstract]
Operating lease expense (a)	$ 105	$ 321
Amortization of right-of-use assets	3	10
Interest on lease liabilities	1	4
Total finance lease expense	4	14
Sublease income	(6)	(20)
Total lease related expenses, net	103	315
short term leases and variable leases costs	31	96
Operating cash flows from operating leases		219
Operating cash flows from finance leases		4
Financing cash flows from finance leases		5
Operating leases		209
Finance leases		27
OPERATING LEASE RIGHT-OF-USE ASSETS	1,103	1,103	$ 0
Operating lease liabilities	210	210	0
LONG-TERM OPERATING LEASE LIABILITIES	991	991	0
Total operating lease liabilities	1,201	1,201
Finance Lease Right-of-Use Asset	165	165
Current finance lease liabilities (included within accounts payable and accrued liabilities)	7	7
Long-term finance lease liabilities (included within other long-term liabilities)	51	51
Total finance lease liabilities	$ 58	$ 58
Weighted average remaining operating lease term (in years)	6 years 9 months 18 days	6 years 9 months 18 days
Weighted average remaining finance lease term (in years)	16 years 3 months 18 days	16 years 3 months 18 days
Weighted average discount rate - operating leases (percentage)	4.50%	4.50%
Weighted average discount rate - finance leases (percentage)	5.70%	5.70%
Lessee, Operating Lease, Liability, Payment, Due [Abstract]
Three months ended December 31, 2019	$ 71	$ 71
2020	280	280
2021	247	247
2022	210	210
2023	182	182
Thereafter	526	526
Undiscounted lease cash flow commitments	1,516	1,516
Reconciling impact from discounting	(315)	(315)
Finance Lease, Liability, Payment, Due [Abstract]
Three months ended December 31, 2019	1	1
2020	6	6
2021	6	6
2022	6	6
2023	5	5
Thereafter	59	59
Undiscounted lease cash flow commitments	83	83
Reconciling impact from discounting finance lease liabilities	$ (25)	$ (25)
Operating Leases, Future Minimum Payments Due, Fiscal Year Maturity [Abstract]
2019			286
2020			254
2021			207
2022			170
2023			143
Thereafter			440
Operating Leases, Future Minimum Payments Due			1,500
Capital Leases, Future Minimum Payments Due, Fiscal Year Maturity [Abstract]
2019			10
2020			9
2021			9
2022			9
2023			10
Thereafter			64
Capital Leases, Future Minimum Payments Due			$ 111