Significant Accounting Policies (Pensions) (Details) - USD ($) $ in Millions	12 Months Ended
	Dec. 31, 2019	Dec. 31, 2018	Dec. 31, 2017
Pension and other postretirement benefits
Recognition period of investment gains or losses related to asset valuation for determining net periodic benefit cost	5 years
Conditional amortization gains or losses as percentage of greater of plan assets or liabilities, minimum	10.00%
Pension liability, current and noncurrent	$ 351	$ 362
Pension asset, non-current	42	47
Net periodic benefit costs (income)	$ (3)	$ (9)	$ 5