New Accounting Standard (Unaudited) Restricted Cash ASU (Details) - USD ($) $ in Millions	3 Months Ended
Mar. 31, 2018	Mar. 31, 2017
New Accounting Pronouncements or Change in Accounting Principle [Line Items]
Payments for (Proceeds from) Other Investing Activities	$ (90)	$ (17)
Net Cash Provided by (Used in) Investing Activities	(492)	(361)
Cash and Cash Equivalents, Period Increase (Decrease)	(711)	(248)
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	3,702
Scenario, Previously Reported [Member]
New Accounting Pronouncements or Change in Accounting Principle [Line Items]
Payments for (Proceeds from) Other Investing Activities		(21)
Net Cash Provided by (Used in) Investing Activities		(365)
Cash and Cash Equivalents, Period Increase (Decrease)		(252)
Cash, cash equivalents, restricted cash and restricted cash equivalents at beginning of year	4,001	4,245
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		4
Net Cash Provided by (Used in) Investing Activities		4
Cash and Cash Equivalents, Period Increase (Decrease)		4
Cash, cash equivalents, restricted cash and restricted cash equivalents at beginning of year	$ 162	$ 158

Amount of currency on hand as well as demand deposits with banks or financial institutions. Includes other kinds of accounts that have the general characteristics of demand deposits. Also includes short-term, highly liquid investments that are both readily convertible to known amounts of cash and so near their maturity that they present insignificant risk of changes in value because of changes in interest rates. Excludes cash and cash equivalents within disposal group and discontinued operation.

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Amount of cash inflow (outflow) from investing activities, including discontinued operations. Investing activity cash flows include making and collecting loans and acquiring and disposing of debt or equity instruments and property, plant, and equipment and other productive assets.

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