Derivative Financial Instruments Netting of Financial Instruments - Derivatives (Details) - USD ($) $ in Millions		Jun. 30, 2018	Dec. 31, 2017
Derivative [Line Items]
Derivative Asset, Fair Value, Gross Asset		$ 3,070	$ 3,904
Derivative Asset, Fair Value, Gross Asset Including Not Subject to Master Netting Arrangement		3,070	3,904
Derivative Asset, Fair Value, Gross Liability and Obligation to Return Cash, Offset		2,503	3,102
Derivative Asset	[1]	567	802
Derivative, Collateral, Obligation to Return Securities		16	28
Derivative Asset, Fair Value, Amount Not Offset Against Collateral		551	774
Derivative Liability, Fair Value, Gross Liability		3,499	4,442
Derivative Liability, Fair Value, Gross Liability Including Not Subject to Master Netting Arrangement		3,499	4,442
Derivative Liability, Fair Value, Gross Asset and Right to Reclaim Cash, Offset		2,869	4,034
Derivative Liability	[2]	630	408
Derivative, Collateral, Right to Reclaim Securities		38	27
Derivative Liability, Fair Value, Amount Not Offset Against Collateral		592	381
Derivatives Subject to Master Netting Arrangement or Similar Arrangement [Member]
Derivative [Line Items]
Derivative Asset, Fair Value, Gross Asset		2,801	3,491
Derivative Asset, Fair Value, Gross Liability and Obligation to Return Cash, Offset		2,386	2,923
Derivative Asset		415	568
Derivative, Collateral, Obligation to Return Securities		16	28
Derivative Asset, Fair Value, Amount Not Offset Against Collateral		399	540
Derivative Liability, Fair Value, Gross Liability		3,272	4,128
Derivative Liability, Fair Value, Gross Asset and Right to Reclaim Cash, Offset		2,752	3,855
Derivative Liability		520	273
Derivative, Collateral, Right to Reclaim Securities		38	27
Derivative Liability, Fair Value, Amount Not Offset Against Collateral		482	246
Derivatives Not Subject to Master Netting Arrangement or Similar Arrangement [Member] [Member]
Derivative [Line Items]
Derivative Asset, Fair Value, Gross Asset		20	18
Derivative Asset, Fair Value, Gross Liability and Obligation to Return Cash, Offset		0	0
Derivative Asset		20	18
Derivative, Collateral, Obligation to Return Securities		0	0
Derivative Asset, Fair Value, Amount Not Offset Against Collateral		20	18
Derivative Liability, Fair Value, Gross Liability		110	130
Derivative Liability, Fair Value, Gross Asset and Right to Reclaim Cash, Offset		0	0
Derivative Liability		110	130
Derivative, Collateral, Right to Reclaim Securities		0	0
Derivative Liability, Fair Value, Amount Not Offset Against Collateral		110	130
Exchange Traded [Member]
Derivative [Line Items]
Derivative Asset, Fair Value, Gross Asset		249	395
Derivative Asset, Fair Value, Gross Liability and Obligation to Return Cash, Offset		117	179
Derivative Asset		132	216
Derivative, Collateral, Obligation to Return Securities		0	0
Derivative Asset, Fair Value, Amount Not Offset Against Collateral		132	216
Derivative Liability, Fair Value, Gross Liability		117	184
Derivative Liability, Fair Value, Gross Asset and Right to Reclaim Cash, Offset		117	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 June 30, 2018, $567 million, net of $467 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 June 30, 2018, $630 million, net of $833 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.