Leases - Other supplemental information (Details) $ in Millions	3 Months Ended
	Mar. 31, 2019 USD ($)
Leases [Abstract]
Operating cash flows from operating leases	$ 88
Operating cash flows from finance leases	15
Financing cash flows from finance leases	10
Right-of-Use Asset Obtained in Exchange for Operating Lease Liability	1,098	[1]
Right-of-Use Asset Obtained in Exchange for Finance Lease Liability	$ 58
Operating Lease, Weighted Average Remaining Lease Term	9 years 2 months 12 days
Finance Lease, Weighted Average Remaining Lease Term	6 years 1 month 6 days
Operating Lease, Weighted Average Discount Rate, Percent	4.70%

[1] Represents operating lease right-of-use assets exchanged for lease obligations upon implementation of the new lease accounting standard on January 1, 2019.