Derivative Financial Instruments Netting of Financial Instruments - Derivatives (Details) - USD ($) $ in Millions		Dec. 31, 2017	Dec. 31, 2016
Derivative [Line Items]
Derivative Asset, Fair Value, Gross Asset		$ 3,904	$ 4,514
Derivative Asset, Fair Value, Gross Asset Including Not Subject to Master Netting Arrangement		3,904	4,514
Derivative Asset, Fair Value, Gross Liability and Obligation to Return Cash, Offset		3,102	3,530
Derivative Asset	[1]	802	984
Derivative, Collateral, Obligation to Return Securities		28	48
Derivative Asset, Fair Value, Amount Not Offset Against Collateral		774	936
Derivative Liability, Fair Value, Gross Liability		4,442	4,902
Derivative Liability, Fair Value, Gross Liability Including Not Subject to Master Netting Arrangement		4,442	4,902
Derivative Liability, Fair Value, Gross Asset and Right to Reclaim Cash, Offset		4,034	4,504
Derivative Liability	[2]	408	398
Derivative, Collateral, Right to Reclaim Securities		27	33
Derivative Liability, Fair Value, Amount Not Offset Against Collateral		381	365
Derivatives Subject to Master Netting Arrangement or Similar Arrangement [Member]
Derivative [Line Items]
Derivative Asset, Fair Value, Gross Asset		3,491	4,193
Derivative Asset, Fair Value, Gross Liability and Obligation to Return Cash, Offset		2,923	3,384
Derivative Asset		568	809
Derivative, Collateral, Obligation to Return Securities		28	48
Derivative Asset, Fair Value, Amount Not Offset Against Collateral		540	761
Derivative Liability, Fair Value, Gross Liability		4,128	4,649
Derivative Liability, Fair Value, Gross Asset and Right to Reclaim Cash, Offset		3,855	4,358
Derivative Liability		273	291
Derivative, Collateral, Right to Reclaim Securities		27	33
Derivative Liability, Fair Value, Amount Not Offset Against Collateral		246	258
Derivatives Not Subject to Master Netting Arrangement or Similar Arrangement [Member] [Member]
Derivative [Line Items]
Derivative Asset, Fair Value, Gross Asset		18	27
Derivative Asset, Fair Value, Gross Liability and Obligation to Return Cash, Offset		0	0
Derivative Asset		18	27
Derivative, Collateral, Obligation to Return Securities		0	0
Derivative Asset, Fair Value, Amount Not Offset Against Collateral		18	27
Derivative Liability, Fair Value, Gross Liability		130	105
Derivative Liability, Fair Value, Gross Asset and Right to Reclaim Cash, Offset		0	0
Derivative Liability		130	105
Derivative, Collateral, Right to Reclaim Securities		0	0
Derivative Liability, Fair Value, Amount Not Offset Against Collateral		130	105
Exchange Traded [Member]
Derivative [Line Items]
Derivative Asset, Fair Value, Gross Asset		395	294
Derivative Asset, Fair Value, Gross Liability and Obligation to Return Cash, Offset		179	146
Derivative Asset		216	148
Derivative, Collateral, Obligation to Return Securities		0	0
Derivative Asset, Fair Value, Amount Not Offset Against Collateral		216	148
Derivative Liability, Fair Value, Gross Liability		184	148
Derivative Liability, Fair Value, Gross Asset and Right to Reclaim Cash, Offset		179	146
Derivative Liability		5	2
Derivative, Collateral, Right to Reclaim Securities		0	0
Derivative Liability, Fair Value, Amount Not Offset Against Collateral		$ 5	$ 2

[1] 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. At December 31, 2016, $984 million, net of $291 million offsetting cash collateral, is recognized in Trading assets and derivative instruments within the Company's Consolidated Balance Sheets.

[2] 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. At December 31, 2016, $398 million, net of $1.3 billion offsetting cash collateral, is recognized in Trading liabilities and derivative instruments within the Company's Consolidated Balance Sheets.