Leases - Maturities (Details) - USD ($) $ in Millions	Dec. 31, 2019	Jan. 01, 2019	Dec. 31, 2018
Maturities of operating lease liabilities
2020	$ 130		$ 141
2021	113		99
2022	84		91
2023	58		67
2024	48		52
Thereafter	164		$ 210
Total undiscounted lease payments	597
Less imputed interest	(114)
Total operating lease liability	483	$ 498
Maturities of finance lease liabilities
2020	7
2021	7
2022	7
2023	7
2024	7
Thereafter	26
Total undiscounted lease payments	61
Less imputed interest	(16)
Total finance lease liability	$ 45
Weighted average discount rate for operating leases	6.58%
Weighted average discount rate for financing leases	6.31%