Fair Value Measurement (Unobservable inputs) (Details) - USD ($) $ in Millions	6 Months Ended
	Jun. 30, 2021	Dec. 31, 2020
Fair Value, Assets Measured on Recurring Basis, Unobservable Input Reconciliation [Line Items]
Other Assets, Current	$ 390	$ 341
Other Assets, Noncurrent	1,528	$ 1,560
Gulf of Mexico Contingent Consideration [Member]
Fair Value, Assets Measured on Recurring Basis, Unobservable Input Reconciliation [Line Items]
Fair Value, Measurement with Unobservable Inputs Reconciliation, Recurring Basis, Asset, Settlements	(10)
Fair Value, Assets Measured on Recurring Basis, Unobservable Input Reconciliation, Calculation [Roll Forward]
Fair value at January 1, 2021	88
Net unrealized gain related to assets still held at the end of the period	7
Fair value at June 30, 2021	$ 85