Accumulated Other Comprehensive Loss - Reclassification (Detail) - USD ($) $ in Millions	3 Months Ended								12 Months Ended
	Dec. 31, 2019	Sep. 30, 2019	Jun. 30, 2019	Mar. 31, 2019	Dec. 31, 2018	Sep. 30, 2018	Jun. 30, 2018	Mar. 31, 2018	Dec. 31, 2019	Dec. 31, 2018	Dec. 31, 2017
Reclassification Adjustment out of Accumulated Other Comprehensive Income [Line Items]
Outstanding derivatives	$ 0				$ 0				$ 0	$ 0	$ 0
Reclassifications for the period, before tax									2,105	2,376	2,191
Reclassifications for the period, net of tax	$ 447	$ 495	$ 382	$ 347	$ 531	$ 498	$ 499	$ 395	1,671	1,923	1,949
Derivative Instruments [Member] | Reclassification out of Accumulated Other Comprehensive Income [Member]
Reclassification Adjustment out of Accumulated Other Comprehensive Income [Line Items]
Reclassifications for the period, before tax									11	11	12
Reclassifications for the period, net of tax									$ 8	$ 8	$ 7