Significant Accounting Policies Significant Accounting Policies Additional Information (Details) - USD ($) $ in Millions	12 Months Ended
	Dec. 31, 2018	Dec. 31, 2017	Dec. 31, 2016
Significant Accounting Policies [Line Items]
Sale Leaseback Transaction, Deferred Gain, Gross	$ 42	$ 49
Operating Leases, Future Minimum Payments Due, Future Minimum Sublease Rentals	1,300
Operating Lease, Right-of-Use Asset	1,200
Adoption of ASU 2016-02 [Member]
Significant Accounting Policies [Line Items]
Sale Leaseback Transaction, Deferred Gain, Gross	31
Cash Proceeds from BOLI/COLI [Member]
Significant Accounting Policies [Line Items]
New Accounting Pronouncement or Change in Accounting Principle, Effect of Adoption, Quantification	14	3	$ 17
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	202	$ 127	202
Contingent Consideration Paid Up to Amount of Acquisition Date Fair Value [Member] [Member]
Significant Accounting Policies [Line Items]
New Accounting Pronouncement or Change in Accounting Principle, Effect of Adoption, Quantification			13
Contingent Consideration Paid in Excess of Acquisition Date Fair Value [Member] [Member]
Significant Accounting Policies [Line Items]
New Accounting Pronouncement or Change in Accounting Principle, Effect of Adoption, Quantification			$ 10
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	(26)
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	$ (26)