New Accounting Standard (Unaudited) Restricted Cash ASU (Details) - USD ($) $ in Millions	6 Months Ended
	Jun. 30, 2018	Jun. 30, 2017
New Accounting Pronouncements or Change in Accounting Principle [Line Items]
Payments for (Proceeds from) Other Investing Activities	$ (86)	$ 3
Net Cash Provided by (Used in) Investing Activities	(970)	(703)
Cash and Cash Equivalents, Period Increase (Decrease)	(569)	422
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 beginning of year	$ 4,106	4,832
Scenario, Previously Reported [Member]
New Accounting Pronouncements or Change in Accounting Principle [Line Items]
Payments for (Proceeds from) Other Investing Activities		(4)
Net Cash Provided by (Used in) Investing Activities		(710)
Cash and Cash Equivalents, Period Increase (Decrease)		415
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 beginning of year		4,667
Accounting Standards Update 2016-18 [Member] | Restatement Adjustment [Member]
New Accounting Pronouncements or Change in Accounting Principle [Line Items]
Payments for (Proceeds from) Other Investing Activities		7
Net Cash Provided by (Used in) Investing Activities		7
Cash and Cash Equivalents, Period Increase (Decrease)		7
Cash, cash equivalents, restricted cash and restricted cash equivalents at beginning of year		158
Cash, cash equivalents, restricted cash and restricted cash equivalents at beginning of year		$ 165