Derivative Financial Instruments and Off-balance sheet Financial Instruments - Gross and net amounts for OTC derivatives (Details) - USD ($) $ in Millions	Dec. 31, 2018	Dec. 31, 2017
Asset derivatives
Asset derivatives gross amount	$ 30	$ 115
Asset derivatives, Gross liability	(2)	0
Total asset derivatives, Fair value, net	28	115
Liability derivatives
Liability derivatives gross amount	(228)	(346)
Liability derivatives, Gross asset	1	3
Derivative liabilities net amount on balance sheet	(227)	(343)
OTC derivatives
Asset derivatives
Asset derivatives gross amount	10	4
Asset derivatives, Gross liability	(3)	(3)
Derivative asset offsets under cash collateral received	(5)	0
Total asset derivatives, Fair value, net	2	1
Derivative assets pledged under securities collateral	0	0
Asset derivatives, net amount	2	1
Liability derivatives
Liability derivatives gross amount	(2)	(10)
Liability derivatives, Gross asset	3	3
Derivative liability offsets under cash collateral pledged	(1)	(2)
Derivative liabilities net amount on balance sheet	0	(9)
Derivative liabilities received under securities collateral	0	3
Liability derivatives, net amount	$ 0	$ (6)