Significant Accounting Policies Significant Accounting Policies Additional Information (Details) - USD ($) $ in Millions	3 Months Ended	6 Months Ended
	Jun. 30, 2018	Jun. 30, 2018	Jun. 30, 2017
Significant Accounting Policies [Line Items]
Sale Leaseback Transaction, Deferred Gain, Gross	$ 42	$ 42
Maximum [Member]
Significant Accounting Policies [Line Items]
Operating Leases, Future Minimum Payments Due, Future Minimum Sublease Rentals	1,500	1,500
Minimum [Member]
Significant Accounting Policies [Line Items]
Operating Leases, Future Minimum Payments Due, Future Minimum Sublease Rentals	1,000	1,000
Cash Premiums Paid on BOLI/COLI [Member] [Member]
Significant Accounting Policies [Line Items]
New Accounting Pronouncement or Change in Accounting Principle, Effect of Adoption, Quantification		1	$ 126
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	4	(7)
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	$ 4	$ (7)