Derivative Instruments - Asset and Liability Management Derivative Positions of Company (Parenthetical) (Detail) - Asset and Liability Management Positions [Member] - USD ($) $ in Millions	9 Months Ended	12 Months Ended
	Sep. 30, 2018	Dec. 31, 2017
Derivative [Line Items]
Notional Value, Assets	$ 37,454	$ 36,579
Notional Value, Liabilities	25,322	21,030
Fair Value, Liabilities	114	172
Underwriting Purchase and Sale Commitments [Member]
Derivative [Line Items]
Notional Value, Assets	103
Notional Value, Liabilities	103
Swap [Member] | Visa Class B Shares [Member]
Derivative [Line Items]
Notional Value, Liabilities	1,400	1,200
Fair Value, Liabilities	$ 89	$ 125
Derivative Liability Average Remaining Maturity Period	1 year 9 months	2 years 6 months