Investments and Related Matters Other Segments (Details) - USD ($) $ in Millions	Sep. 30, 2018	Dec. 31, 2017
Schedule of Investments [Line Items]
Investments	$ 9,332	$ 10,038
Other Segments
Schedule of Investments [Line Items]
Investments	621	506
Other Segments | Equity method investments
Schedule of Investments [Line Items]
Investments	127	106
Other Segments | Other investments (measured at fair value)
Schedule of Investments [Line Items]
Investments	$ 494	$ 400