Derivative Financial Instruments Netting of Financial Instruments - Derivatives (Details) - USD ($) $ in Millions		Mar. 31, 2018	Dec. 31, 2017
Derivative [Line Items]
Derivative Asset, Fair Value, Gross Asset		$ 3,074	$ 3,904
Derivative Asset, Fair Value, Gross Asset Including Not Subject to Master Netting Arrangement		3,074	3,904
Derivative Asset, Fair Value, Gross Liability and Obligation to Return Cash, Offset		2,417	3,102
Derivative Asset	[1]	657	802
Derivative, Collateral, Obligation to Return Securities		18	28
Derivative Asset, Fair Value, Amount Not Offset Against Collateral		639	774
Derivative Liability, Fair Value, Gross Liability		3,505	4,442
Derivative Liability, Fair Value, Gross Liability Including Not Subject to Master Netting Arrangement		3,505	4,442
Derivative Liability, Fair Value, Gross Asset and Right to Reclaim Cash, Offset		2,925	4,034
Derivative Liability	[2]	580	408
Derivative, Collateral, Right to Reclaim Securities		34	27
Derivative Liability, Fair Value, Amount Not Offset Against Collateral		546	381
Derivatives Subject to Master Netting Arrangement or Similar Arrangement [Member]
Derivative [Line Items]
Derivative Asset, Fair Value, Gross Asset		2,805	3,491
Derivative Asset, Fair Value, Gross Liability and Obligation to Return Cash, Offset		2,279	2,923
Derivative Asset		526	568
Derivative, Collateral, Obligation to Return Securities		18	28
Derivative Asset, Fair Value, Amount Not Offset Against Collateral		508	540
Derivative Liability, Fair Value, Gross Liability		3,253	4,128
Derivative Liability, Fair Value, Gross Asset and Right to Reclaim Cash, Offset		2,787	3,855
Derivative Liability		466	273
Derivative, Collateral, Right to Reclaim Securities		34	27
Derivative Liability, Fair Value, Amount Not Offset Against Collateral		432	246
Derivatives Not Subject to Master Netting Arrangement or Similar Arrangement [Member] [Member]
Derivative [Line Items]
Derivative Asset, Fair Value, Gross Asset		17	18
Derivative Asset, Fair Value, Gross Liability and Obligation to Return Cash, Offset		0	0
Derivative Asset		17	18
Derivative, Collateral, Obligation to Return Securities		0	0
Derivative Asset, Fair Value, Amount Not Offset Against Collateral		17	18
Derivative Liability, Fair Value, Gross Liability		114	130
Derivative Liability, Fair Value, Gross Asset and Right to Reclaim Cash, Offset		0	0
Derivative Liability		114	130
Derivative, Collateral, Right to Reclaim Securities		0	0
Derivative Liability, Fair Value, Amount Not Offset Against Collateral		114	130
Exchange Traded [Member]
Derivative [Line Items]
Derivative Asset, Fair Value, Gross Asset		252	395
Derivative Asset, Fair Value, Gross Liability and Obligation to Return Cash, Offset		138	179
Derivative Asset		114	216
Derivative, Collateral, Obligation to Return Securities		0	0
Derivative Asset, Fair Value, Amount Not Offset Against Collateral		114	216
Derivative Liability, Fair Value, Gross Liability		138	184
Derivative Liability, Fair Value, Gross Asset and Right to Reclaim Cash, Offset		138	179
Derivative Liability		0	5
Derivative, Collateral, Right to Reclaim Securities		0	0
Derivative Liability, Fair Value, Amount Not Offset Against Collateral		$ 0	$ 5

[1] At March 31, 2018, $657 million, net of $408 million offsetting cash collateral, is recognized in Trading assets and derivative instruments within the Company's Consolidated Balance Sheets. At December 31, 2017, $802 million, net of $371 million offsetting cash collateral, is recognized in Trading assets and derivative instruments within the Company's Consolidated Balance Sheets.

[2] At March 31, 2018, $580 million, net of $916 million offsetting cash collateral, is recognized in Trading liabilities and derivative instruments within the Company's Consolidated Balance Sheets. At December 31, 2017, $408 million, net of $1.3 billion offsetting cash collateral, is recognized in Trading liabilities and derivative instruments within the Company's Consolidated Balance Sheets.