Derivative Instruments - Asset and Liability Management Derivative Positions of Company (Parenthetical) (Detail) - Asset and Liability Management Positions [Member] - USD ($) $ in Millions	3 Months Ended	12 Months Ended
	Mar. 31, 2018	Dec. 31, 2017
Derivative [Line Items]
Notional Value, Assets	$ 41,815	$ 36,579
Notional Value, Liabilities	22,221	21,030
Fair Value, Liabilities	305	172
Underwriting Purchase and Sale Commitments [Member]
Derivative [Line Items]
Notional Value, Assets	300
Notional Value, Liabilities	300
Swap [Member] | Visa Class B Shares [Member]
Derivative [Line Items]
Notional Value, Liabilities	1,200	1,200
Fair Value, Liabilities	$ 122	$ 125
Derivative Liability Average Remaining Maturity Period	2 years 2 months 30 days	2 years 6 months