Derivative Instruments (Current Period Cash Flow Hedges in AOCI (loss) before Taxes) (Details) - USD ($) $ in Millions	12 Months Ended
	Dec. 31, 2019	Dec. 31, 2018	Dec. 31, 2017	Jan. 01, 2019	[1]	Jan. 01, 2017
Reclassification Adjustment out of Accumulated Other Comprehensive Income on Derivatives [Line Items]
Cumulative Effect of New Accounting Principle in Period of Adoption		$ 9		$ (14)		$ 0
Cash flow hedges in AOCI
Reclassification Adjustment out of Accumulated Other Comprehensive Income on Derivatives [Line Items]
Balance, beginning	$ 811	(39)	$ 1,316
Net deferred gains/(losses) on cash flow hedges for the reporting period	391	1,401	(1,373)
Amount reclassified into current period earnings	(379)	(551)	18
Ending Balance	832	811	(39)
Interest Rate | Cash flow hedges in AOCI
Reclassification Adjustment out of Accumulated Other Comprehensive Income on Derivatives [Line Items]
Net deferred gains/(losses) on cash flow hedges for the reporting period	33	33	5
Amount reclassified into current period earnings	(58)	(1)	2
Currency | Cash flow hedges in AOCI
Reclassification Adjustment out of Accumulated Other Comprehensive Income on Derivatives [Line Items]
Net deferred gains/(losses) on cash flow hedges for the reporting period	(56)	27	(3)
Amount reclassified into current period earnings	(6)	(7)	0
Currency/Interest Rate | Cash flow hedges in AOCI
Reclassification Adjustment out of Accumulated Other Comprehensive Income on Derivatives [Line Items]
Net deferred gains/(losses) on cash flow hedges for the reporting period	414	1,341	(1,375)
Amount reclassified into current period earnings	$ (315)	$ (543)	$ 16

[1] Includes the impact from the adoption of ASU 2017-08 and 2017-12. See Note 2.