Derivative Financial Instruments - Gross and net amounts for OTC derivatives (Details) - USD ($) $ in Millions	Sep. 30, 2018	Dec. 31, 2017
Asset derivatives
Asset derivatives gross amount	$ 120	$ 127
Asset derivatives, gross liability	(5)	(1)
Derivative assets net amount on balance sheet	115	126
Liability derivatives
Liability derivatives gross amount	(308)	(369)
Liability derivatives, gross asset	1	6
Derivative liabilities net amount on balance sheet	(307)	(363)
OTC derivatives
Asset derivatives
Asset derivatives gross amount	16	8
Asset derivatives, gross liability	(6)	(7)
Derivative, collateral, right to reclaim cash	(7)	1
Derivative assets net amount on balance sheet	3	2
Derivative assets received under securities collateral	0	0
Derivative asset, fair value, amount offset against collateral	3	2
Liability derivatives
Liability derivatives gross amount	(8)	(26)
Liability derivatives, gross asset	6	7
Derivative liability offsets under cash collateral pledged	0	7
Derivative liabilities net amount on balance sheet	(2)	(12)
Derivative liabilities received under securities collateral	0	3
Derivative liability, fair value, amount offset against collateral	$ (2)	$ (9)