Casualty, Environmental and Other Reserves - Narrative (Details)	1 Months Ended	2 Months Ended	3 Months Ended		6 Months Ended
	Jun. 30, 2018 USD ($) claim site	May 31, 2018 USD ($)	Jun. 30, 2018 USD ($) claim site $ / shares	Jun. 30, 2017 USD ($) $ / shares	Jun. 30, 2018 USD ($) claim site $ / shares	Jun. 30, 2017 USD ($) $ / shares	Dec. 31, 2017 USD ($)
All Contingencies Reserves [Line Items]
Total reserves	$ 346,000,000		$ 346,000,000		$ 346,000,000		$ 374,000,000
Net Earnings			$ 877,000,000	$ 510,000,000	$ 1,572,000,000	$ 872,000,000
Net Earnings Per Share, Basic (in dollars per share) | $ / shares			$ 1.02	$ 0.55	$ 1.80	$ 0.94
Casualty
All Contingencies Reserves [Line Items]
Total reserves	201,000,000		$ 201,000,000		$ 201,000,000		228,000,000
Self-insured retention amount, per occurrence	$ 75,000,000	$ 50,000,000
Number of individual claims expected to exceed self insured retention amount | claim	0		0		0
Environmental
All Contingencies Reserves [Line Items]
Total reserves	$ 91,000,000		$ 91,000,000		$ 91,000,000		90,000,000
Environmental impaired sites | site	218		218		218
Other
All Contingencies Reserves [Line Items]
Total reserves	$ 54,000,000		$ 54,000,000		$ 54,000,000		$ 56,000,000