Components of Accumulated Other Comprehensive Loss, Net - MEC (Details) - USD ($) $ in Millions	3 Months Ended		6 Months Ended
	Jun. 30, 2019	Jun. 30, 2018	Jun. 30, 2019	Jun. 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	$ (27)	$ 3	(35)	$ 1
Other comprehensive income (loss)	(58)	(250)	57	(182)
Ending balance - Accumulated other comprehensive loss, net	(1,888)		(1,888)
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			(35)	1
Other comprehensive income (loss)	(58)	(250)	57	(182)
Ending balance - unrealized gains (losses) on available-for-sale securities	0	0	0	0
Ending balance - unrealized gains (losses) on cash flow hedges	1	30	1	30
Ending balance - Accumulated other comprehensive loss, net	$ (1,888)	$ (1,665)	$ (1,888)	$ (1,665)