Casualty, Environmental and Other Reserves - Schedule of Claims Activity (Details) - USD ($) $ in Millions	12 Months Ended
	Dec. 31, 2020	Dec. 31, 2019	Dec. 31, 2018
Loss Contingency Accrual [Roll Forward]
Balance at beginning of period	$ 305	$ 324	$ 374
Charged to Expense	107	107	72
Payments	(98)	(126)	(122)
Balance end of period	314	305	324
Casualty Reserves
Loss Contingency Accrual [Roll Forward]
Balance at beginning of period	187	199	228
Charged to Expense	55	56	21
Payments	(46)	(68)	(50)
Balance end of period	196	187	199
Environmental Reserves
Loss Contingency Accrual [Roll Forward]
Balance at beginning of period	74	80	90
Charged to Expense	20	17	10
Payments	(18)	(23)	(20)
Balance end of period	76	74	80
Other Reserves
Loss Contingency Accrual [Roll Forward]
Balance at beginning of period	44	45	56
Charged to Expense	32	34	41
Payments	(34)	(35)	(52)
Balance end of period	$ 42	$ 44	$ 45