Fair Value of Assets and Liabilities Fair Value of Assets & Liabilities (Non-Recurring) (Details) - Nonconsolidated VIEs [Member] - Affordable housing partnerships [Member] - USD ($) $ in Millions	Dec. 31, 2018	Dec. 31, 2017
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Affordable housing partnerships, carrying value	$ 352	$ 408
Nonrecurring basis [Member] \| Level 3 [Member]
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Affordable housing partnerships, carrying value	$ 112	$ 166

Carrying amount of the assets in the reporting entity's statement of financial position that relate to the reporting entity's variable interest in the Variable Interest Entity (VIE), where the reporting entity is not the VIE's primary beneficiary.

Reference 1: http://fasb.org/us-gaap/role/ref/legacyRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 810
-SubTopic 10
-Section 50
-Paragraph 4
-Subparagraph a
-URI http://asc.fasb.org/extlink&oid=108788376&loc=d3e5728-111685

Name:	us-gaap_VariableInterestEntityNonconsolidatedCarryingAmountAssets
Namespace Prefix:	us-gaap_
Data Type:	xbrli:monetaryItemType
Balance Type:	debit
Period Type:	instant