Derivative and Hedging Activities - Cash Flow Hedges Components of AOCI Table (Details) - USD ($) $ in Millions	3 Months Ended
	Mar. 31, 2019	Mar. 31, 2018
AOCI Attributable to Parent, Net of Tax [Roll Forward]
AOCI, after tax, beginning of period	$ (23)
Losses reclassified to income, after tax	10	$ 10	[1],[2]
AOCI, after tax, end of period	(13)
Cash flow hedging
AOCI Attributable to Parent, Net of Tax [Roll Forward]
AOCI, before tax, beginning of period	(80)	(114)
AOCI, after tax, beginning of period	(23)	(57)
Losses reclassified to income, before tax	10	10
Losses reclassified to income, after tax	10	10
AOCI, before tax, end of period	(70)	(104)
AOCI, after tax, end of period	$ (13)	$ (47)

[1] Deferred tax activity incurred in other comprehensive income was offset by a valuation allowance.

[2] Financial information for 2018 has been recast to reflect the retrospective application of the successful efforts method of accounting. See Note 1.