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Amount of cash inflow from sale of investment in debt security measured at fair value with change in fair value recognized in other comprehensive income (available-for-sale).

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Marketable and Other Securities - Narrative (Details) - USD ($) $ in Millions	12 Months Ended
	Dec. 31, 2018	Dec. 31, 2017	Dec. 31, 2016
Marketable Securities [Line Items]
Sales proceeds from investments classified as available-for-sale and sold prior to maturity	$ 4,300	$ 5,600	$ 8,500
Level 3 [Member]
Marketable Securities [Line Items]
Fair value of equity securities	884
Level 3 [Member] \| Interest Income and Other Non-Operating Income, Net [Member]
Marketable Securities [Line Items]
Unrealized gain on equity securities	$ 142