Contingencies and Commitments - Leases (Details) - USD ($) $ in Millions	3 Months Ended	12 Months Ended
	Mar. 31, 2020	Dec. 31, 2019
Commitments and Contingencies Disclosure [Abstract]
Right-of-use assets	$ 393	$ 384
Lease liabilities, current	89	86
Lease liabilities, non-current	$ 306	$ 301
Other information
Weighted-average remaining lease term	5 years 10 months 24 days	6 years 2 months 12 days
Weighted-average discount rate	3.09%	3.34%
Operating lease cost	$ 36	$ 34