Investments (Narrative) (Details) $ in Millions	Mar. 31, 2019 USD ($)	Dec. 31, 2018 USD ($)
Investment [Line Items]
Equity Securities, FV-NI and without Readily Determinable Fair Value	$ 2,000	$ 2,000
Available-for-sale, Securities in Unrealized Loss Positions, Qualitative Disclosure, Number of Positions	11,000
Total number of security positions	30,000
Equity Method Investments	$ 1,500	$ 1,500