New Accounting Standard (Unaudited) Restricted Cash ASU (Details) - USD ($) $ in Millions	9 Months Ended
	Sep. 30, 2018	Sep. 30, 2017
New Accounting Pronouncements or Change in Accounting Principle [Line Items]
Accrued income taxes and timing of other tax payments	$ (131)	$ 393
Net cash provided by operating activities	3,925	3,012
Payments for (Proceeds from) Other Investing Activities	(91)	(2)
Net Cash Provided by (Used in) Investing Activities	(1,472)	(954)
Cash and Cash Equivalents, Period Increase (Decrease)	113	771
Cash, cash equivalents, restricted cash and restricted cash equivalents at beginning of year	4,631	4,403
Cash, cash equivalents, restricted cash and restricted cash equivalents at end of period	$ 4,799	5,129
Restatement Adjustment [Member] | Accounting Standards Update 2016-18 [Member]
New Accounting Pronouncements or Change in Accounting Principle [Line Items]
Accrued income taxes and timing of other tax payments		(6)
Net cash provided by operating activities		(6)
Payments for (Proceeds from) Other Investing Activities		20
Net Cash Provided by (Used in) Investing Activities		20
Cash and Cash Equivalents, Period Increase (Decrease)		14
Cash, cash equivalents, restricted cash and restricted cash equivalents at beginning of year		158
Cash, cash equivalents, restricted cash and restricted cash equivalents at end of period		172
Previously Reported [Member]
New Accounting Pronouncements or Change in Accounting Principle [Line Items]
Accrued income taxes and timing of other tax payments		399
Net cash provided by operating activities		3,018
Payments for (Proceeds from) Other Investing Activities		(22)
Net Cash Provided by (Used in) Investing Activities		(974)
Cash and Cash Equivalents, Period Increase (Decrease)		757
Cash, cash equivalents, restricted cash and restricted cash equivalents at beginning of year		4,245
Cash, cash equivalents, restricted cash and restricted cash equivalents at end of period		$ 4,957