Fair Value Measurement - Equity Securities Without Readily Determinable Fair Value (Details) shares in Millions, $ in Millions	3 Months Ended	6 Months Ended
	Jun. 30, 2018 USD ($) shares	Jun. 30, 2018 USD ($) shares
Fair Value Disclosures [Abstract]
Carrying value	$ 1,471	$ 1,471
Upward carrying value changes	67	562
Downward carrying value changes/impairment	$ (26)	$ (28)
Common stock | Class B | VISA
Investment Holdings [Line Items]
Interest owned, included in other assets (in shares) | shares	40	40
Conversion rate	1.6298	1.6298