Financial Instruments (Derivative) (Details) - USD ($) $ in Millions	Mar. 31, 2018	Dec. 31, 2017	Mar. 31, 2017	Dec. 31, 2016
Cash and Cash Equivalents [Line Items]
Cash, cash equivalents, restricted cash and restricted cash equivalents at end of period	$ 3,702	$ 4,447
Restricted Cash and Cash Equivalents, Current	123	52
Restricted Cash and Cash Equivalents, Noncurrent	127	132
Cash, cash equivalents, restricted cash and restricted cash equivalents at beginning of year	3,952	4,631	$ 4,163	$ 4,403
Credit Derivative, Maximum Exposure, Undiscounted	11
Bank Time Deposits [Member]
Cash and Cash Equivalents [Line Items]
Cash, cash equivalents, restricted cash and restricted cash equivalents at end of period	$ 2,800	$ 2,900