Derivative Instruments - Asset and Liability Management Derivative Positions of Company (Parenthetical) (Detail) - Asset and Liability Management Positions [Member] - USD ($) $ in Millions	6 Months Ended	12 Months Ended
	Jun. 30, 2018	Dec. 31, 2017
Derivative [Line Items]
Notional Value, Assets	$ 42,650	$ 36,579
Notional Value, Liabilities	19,358	21,030
Fair Value, Liabilities	151	172
Underwriting Purchase and Sale Commitments [Member]
Derivative [Line Items]
Notional Value, Assets	147
Notional Value, Liabilities	147
Swap [Member] | Visa Class B Shares [Member]
Derivative [Line Items]
Notional Value, Liabilities	1,300	1,200
Fair Value, Liabilities	$ 119	$ 125
Derivative Liability Average Remaining Maturity Period	2 years 4 days	2 years 6 months