Derivative Instruments - Cumulative Fair Value Hedging Adjustments (Details) - USD ($) $ in Millions	Jun. 30, 2019	Dec. 31, 2018
Commodity contracts
Assets
Carrying amount of the hedged items	$ 6,600	$ 6,800
Long-term debt
Liabilities
Carrying amount of the hedged items	151,184	139,915
Cumulative amount of fair value hedging adjustments included in the carrying amount of hedged items:
Active hedging relationships	6,534	141
Discontinued hedging relationships	55	8
Total	6,589	149
Long-term debt | Not designated as hedges
Liabilities
Carrying amount of the hedged items	6,000	7,300
Beneficial interests issued by consolidated VIEs
Liabilities
Carrying amount of the hedged items	5,208	6,987
Cumulative amount of fair value hedging adjustments included in the carrying amount of hedged items:
Active hedging relationships	0	0
Discontinued hedging relationships	(15)	(33)
Total	(15)	(33)
Investment securities - AFS
Assets
Carrying amount of the hedged items	91,668	55,313
Cumulative amount of fair value hedging adjustments included in the carrying amount of hedged items:
Active hedging relationships	2,084	(1,105)
Discontinued hedging relationships	292	381
Total	2,376	(724)
Investment securities - AFS | Not designated as hedges
Assets
Carrying amount of the hedged items	$ 14,400	$ 14,600