Derivatives (Estimated Fair Value of Derivative Assets and Liabilities after Master Netting Agreements and Cash Collateral) (Details) - USD ($) $ in Millions	Dec. 31, 2016	Dec. 31, 2015
Offsetting Assets [Line Items]
Derivative Asset, Fair Value, Gross Asset Excluding Accruals	$ 16,010	$ 14,684
Derivative Liability, Fair Value, Gross Liability Excluding Accruals	10,712	7,090
Amounts offset in the consolidated balance sheet, Assets	0	0
Amounts offset in the consolidated balance sheet, Liabilities	0	0
Estimated fair value of derivative assets presented in the consolidated balance sheets	16,010	14,684
Estimated fair value of derivative liabilities presented in the consolidated balance sheets	10,712	7,090
Net amount of derivative assets after application of master netting agreements and cash collateral	526	519
Net amount of derivative liabilities after application of master netting agreements and cash collateral	38	86
Over the Counter [Member]
Offsetting Assets [Line Items]
Derivative Asset, Fair Value, Gross Asset Excluding Accruals	13,387	13,017
Derivative Liability, Fair Value, Gross Liability Excluding Accruals	8,650	5,848
Gross estimated fair value of derivative assets	(6,018)	(4,368)
Gross estimated fair value of derivative liabilities	(6,018)	(4,368)
Cash collateral on derivative assets	(4,897)	(6,140)
Cash collateral on derivative liabilities	(84)	(7)
Securities collateral on derivative assets	(2,069)	(2,078)
Securities collateral on derivative liabilities	(2,516)	(1,395)
Exchange Traded [Member]
Offsetting Assets [Line Items]
Derivative Asset, Fair Value, Gross Asset Excluding Accruals	80	67
Derivative Liability, Fair Value, Gross Liability Excluding Accruals	15	25
Gross estimated fair value of derivative assets	(5)	(1)
Gross estimated fair value of derivative liabilities	(5)	(1)
Cash collateral on derivative assets	0	0
Cash collateral on derivative liabilities	(9)	(20)
Securities collateral on derivative assets	0	0
Securities collateral on derivative liabilities	0	(3)
Cleared [Member]
Offsetting Assets [Line Items]
Derivative Asset, Fair Value, Gross Asset Excluding Accruals	2,543	1,600
Derivative Liability, Fair Value, Gross Liability Excluding Accruals	2,047	1,217
Gross estimated fair value of derivative assets	(1,068)	(1,200)
Gross estimated fair value of derivative liabilities	(1,068)	(1,200)
Cash collateral on derivative assets	(1,427)	(378)
Cash collateral on derivative liabilities	(974)	(10)
Securities collateral on derivative assets	0	0
Securities collateral on derivative liabilities	$ 0	$ 0