Commitments and Contingencies Environmental (Details) $ in Millions	6 Months Ended
	Jun. 30, 2019 USD ($) sites	Jun. 30, 2018 USD ($)	Dec. 31, 2018 USD ($)	Dec. 31, 2017 USD ($)
Accrual for Environmental Loss Contingencies [Roll Forward]
Cash and Cash Equivalents, at Carrying Value	$ 1,994	$ 2,139	$ 1,985	$ 1,975
Environmental Issue [Member]
Loss Contingencies [Line Items]
Number of alleged environmental contamination sites (in sites) | sites	200
Accrued obligations for environmental matters, current liabilities	$ 40	40	40
Accrual for Environmental Loss Contingencies [Roll Forward]
Beginning balance	298	317
Accruals / changes in estimates	2	2
Payments	(11)	(9)
Ending balance	$ 289	$ 310
Site Contingency, Estimated Time Frame for Accrued Cost Distributions	10
Environmental Issue [Member] | Minimum [Member]
Loss Contingencies [Line Items]
Future costs to settle claims and associated liability	$ 235
Environmental Issue [Member] | Maximum [Member]
Loss Contingencies [Line Items]
Future costs to settle claims and associated liability	385
BNSF Insurance Company [Member] | Commercial Paper, Bank Time Deposits, and Money Market Funds [Member]
Accrual for Environmental Loss Contingencies [Roll Forward]
Cash and Cash Equivalents, at Carrying Value	$ 514		$ 519