Offsetting Assets and Liabilities (Details) - USD ($) $ in Millions	Sep. 30, 2018	Dec. 31, 2017
Offsetting Assets and Liabilities [Line Items]
Derivative asset, gross amount of recognized assets	$ 70	$ 39
Derivative liability, gross amounts of recognized liabilities	70	41
Customer securities, entity has right to sell or repledge, fair value	12	2
Derivative assets in net asset positions
Offsetting Assets and Liabilities [Line Items]
Derivative asset, gross amount of recognized assets	69	38
Derivative assets and liabilities, gross amounts offset	0	0
Derivative asset, fair value, net amounts offset against collateral	69	38
Derivative asset, gross amounts not offset	0	0
Derivative assets, collateral	0	0
Derivative assets, net	69	38
Derivative assets with no offsetting arrangements
Offsetting Assets and Liabilities [Line Items]
Derivative asset, gross amount of recognized assets	1	1
Derivative assets and liabilities, gross amounts offset	0	0
Derivative asset, fair value, net amounts offset against collateral	1	1
Derivative asset, gross amounts not offset	0	0
Derivative assets, collateral	0	0
Derivative assets, net	1	1
Derivative assets
Offsetting Assets and Liabilities [Line Items]
Derivative asset, gross amount of recognized assets	70	39
Derivative assets and liabilities, gross amounts offset	0	0
Derivative asset, fair value, net amounts offset against collateral	70	39
Derivative asset, gross amounts not offset	0	0
Derivative assets, collateral	0	0
Derivative assets, net	70	39
Derivative liabilities in net liability positions
Offsetting Assets and Liabilities [Line Items]
Derivative assets and liabilities, gross amounts offset	0	0
Derivative liability, gross amounts of recognized liabilities	70	41
Derivative liability, fair value, net amounts offset against collateral	70	41
Derivative liability, gross amounts not offset	0	0
Derivative liabilities, collateral	0	(1)
Derivative liabilities, net	70	40
Securities sold under agreements to repurchase
Offsetting Assets and Liabilities [Line Items]
Derivative assets and liabilities, gross amounts offset	0	0
Derivative liability, gross amounts of recognized liabilities	1,238	892
Derivative liability, fair value, net amounts offset against collateral	1,238	892
Derivative liability, gross amounts not offset	0	0
Derivative liabilities, collateral	(1,238)	(892)
Derivative liabilities, net	0	0
Derivative liabilities
Offsetting Assets and Liabilities [Line Items]
Derivative assets and liabilities, gross amounts offset	0	0
Derivative liability, gross amounts of recognized liabilities	1,308	933
Derivative liability, fair value, net amounts offset against collateral	1,308	933
Derivative liability, gross amounts not offset	0	0
Derivative liabilities, collateral	(1,238)	(893)
Derivative liabilities, net	$ 70	$ 40