Significant Accounting Policies Significant Accounting Policies Additional Information (Details) $ in Millions	3 Months Ended
	Mar. 31, 2018 USD ($)
Minimum [Member]
Significant Accounting Policies [Line Items]
Operating Leases, Future Minimum Payments Due, Future Minimum Sublease Rentals	$ 1,000
Stranded Tax Effects in AOCI, Gross Portion [Member]
Significant Accounting Policies [Line Items]
New Accounting Pronouncement or Change in Accounting Principle, Effect of Adoption, Quantification	182
Stranded Tax Effects in AOCI, Offset Portion [Member]
Significant Accounting Policies [Line Items]
New Accounting Pronouncement or Change in Accounting Principle, Effect of Adoption, Quantification	28
Stranded Tax Effects in AOCI [Member]
Significant Accounting Policies [Line Items]
New Accounting Pronouncement or Change in Accounting Principle, Effect of Adoption, Quantification	154
ASU 2014-09 Revenue from Contracts with Customers - Impact on Noninterest Income [Domain]
Significant Accounting Policies [Line Items]
New Accounting Pronouncement or Change in Accounting Principle, Effect of Adoption, Quantification	(3)
ASU 2014-09 Revenue from Contracts with Customers - Impact on Noninterest Expense [Domain]
Significant Accounting Policies [Line Items]
New Accounting Pronouncement or Change in Accounting Principle, Effect of Adoption, Quantification	$ (3)