Components of Accumulated Other Comprehensive Loss, Net - MEC (Details) - USD ($) $ in Millions	3 Months Ended		9 Months Ended
	Sep. 30, 2019	Sep. 30, 2018	Sep. 30, 2019	Sep. 30, 2018
Accumulated Other Comprehensive Income (Loss) [Roll Forward]
Beginning balance - Accumulated other comprehensive loss, net			$ (1,945)
Other comprehensive income (loss), unrealized gains (losses) on cash flow hedges	$ 7	$ 1	(28)	$ 2
Other comprehensive income (loss)	(191)	(2)	(134)	(184)
Ending balance - Accumulated other comprehensive loss, net	(2,079)		(2,079)
Accumulated Other Comprehensive (Loss) Income, Net [Member]
Accumulated Other Comprehensive Income (Loss) [Roll Forward]
Beginning balance - unrealized gains (losses) on available-for-sale securities			0	1,085
Beginning balance - unrealized gains (losses) on cash flow hedges			36	29
Beginning balance - Accumulated other comprehensive loss, net			(1,945)	(398)
Other comprehensive income (loss), unrealized gains on available-for-sale securities			0	0
Other comprehensive income (loss), unrealized gains (losses) on cash flow hedges			(28)	2
Other comprehensive income (loss)	(191)	(2)	(134)	(184)
Ending balance - unrealized gains (losses) on available-for-sale securities	0	0	0	0
Ending balance - unrealized gains (losses) on cash flow hedges	8	31	8	31
Ending balance - Accumulated other comprehensive loss, net	$ (2,079)	$ (1,667)	$ (2,079)	$ (1,667)