Consolidated Balance Sheets (Parenthetical) - USD ($) $ in Millions	12 Months Ended
	Dec. 31, 2017	Dec. 31, 2016	Dec. 31, 2015
Card Member receivables, gross	$ 54,047.0	$ 47,308.0
Card Member loans	73,399.0	65,265.0
Other assets	9,755.0	10,561.0
Short-term borrowings	3,278.0	5,581.0
Long-term debt	55,804.0	46,990.0
Cash and cash equivalents
Securities purchased under resale agreements	48.0	115.0
Card Member loans and receivables held for sale	0.0	0.0
Accounts receivable
Card Member receivables, reserves	521.0	467.0	$ 462.0
Other receivables, reserves	31.0	45.0
Loans
Balance, January 1	1,706.0	1,223.0	1,028.0
Other loans, reserves	80.0	42.0
Premises and equipment, accumulated depreciation	5,455.0	5,145.0
Restricted cash	336.0	286.0
Accumulated other comprehensive income (loss)
Net unrealized securities gains, tax	1.0	5.0	(20.0)
Net investment hedges	(215.0)	139.0	$ 340.0
Foreign currency translation adjustments, tax	(363.0)	24.0
Net unrealized pension and other postretirement benefit losses, net of tax	$ 179.0	$ 186.0
Common shares, par value	$ 0.2	$ 0.2
Common shares, authorized	3,600,000,000	3,600,000,000	3,600,000,000
Common shares, issued	859,000,000	904,000,000	969,000,000
Common shares, outstanding	859,000,000	904,000,000
Preferred shares, authorized	20,000,000	20,000,000
Preferred shares, issued	1,600	1,600	0
Preferred shares, outstanding	1,600	1,600	0
Preferred shares, par value	$ 1.67	$ 1.67
Variable Interest Enterprise [Member]
Card Member receivables, gross	$ 8,919.0	$ 8,874.0
Card Member loans	25,695.0	26,129.0
Long-term debt	18,560.0	15,113.0
Cash and cash equivalents
Card Member loans and receivables held for sale	0.0	0.0
Loans
Restricted cash	$ 62.0	$ 38.0