Business, Basis of Presentation and Summary of Significant Accounting Policies (Narrative) (Details) $ in Millions	3 Months Ended	9 Months Ended
	Sep. 30, 2017 USD ($)	Sep. 30, 2017 USD ($) Segment	Mar. 31, 2017 USD ($)	Dec. 31, 2016 USD ($)
Organization, Consolidation and Presentation of Financial Statements [Abstract]
Number of segments | Segment		5
New Accounting Pronouncements or Change in Accounting Principle [Line Items]
Premiums and Other Receivables, Net	$ 18,588	$ 18,588		$ 15,445
Payables For Collateral Under Securities Loaned And Other Transactions	27,132	27,132		25,873
Derivative assets	8,792	8,792		12,139
Derivative liabilities	4,668	4,668		6,921
Accrued Investment Income Receivable	3,692	3,692		3,308
Other Liabilities	26,745	$ 26,745		$ 23,700
CME update impact [Member]
New Accounting Pronouncements or Change in Accounting Principle [Line Items]
Premiums and Other Receivables, Net			$ 991
Payables For Collateral Under Securities Loaned And Other Transactions			816
Derivative assets			1,800
Derivative liabilities			2,000
Accrued Investment Income Receivable			101
Other Liabilities			$ 14
Accounting Standards Update 2016-01 [Member]
New Accounting Pronouncements or Change in Accounting Principle [Line Items]
New Accounting Pronouncement or Change in Accounting Principle, Effect of Change on Equity	$ 250