Derivatives and Hedging Activities - Derivative Instrument Cash Flow Hedge Earning Recognized by Income Statement Location (Details) - USD ($)	12 Months Ended
Dec. 31, 2018	Dec. 31, 2017	Dec. 31, 2016
Derivatives, Fair Value [Line Items]
Net Gains (Losses) Recognized in OCI	$ 9,000,000	$ (77,000,000)	$ 28,000,000
Net Gains (Losses) Reclassified From OCI Into Income	(37,000,000)	15,000,000	81,000,000
Net Gains (Losses) Recognized in Other Income(a)	0	0	0
Interest Income [Member] \| Interest Rate [Member] \| Cash Flow Hedges [Member]
Derivatives, Fair Value [Line Items]
Net Gains (Losses) Recognized in OCI	(13,000,000)	(59,000,000)	29,000,000
Net Gains (Losses) Reclassified From OCI Into Income	(68,000,000)	19,000,000	85,000,000
Net Gains (Losses) Recognized in Other Income(a)	0	0	0
Interest Expense [Member] \| Interest Rate [Member] \| Cash Flow Hedges [Member]
Derivatives, Fair Value [Line Items]
Net Gains (Losses) Recognized in OCI	2,000,000	0	0
Net Gains (Losses) Reclassified From OCI Into Income	(2,000,000)	(4,000,000)	(4,000,000)
Net Gains (Losses) Recognized in Other Income(a)	0	0	0
Underwriting Discounts Fees And Commissions [Member] \| Interest Rate [Member] \| Cash Flow Hedges [Member]
Derivatives, Fair Value [Line Items]
Net Gains (Losses) Recognized in OCI	1,000,000	(1,000,000)	1,000,000
Net Gains (Losses) Reclassified From OCI Into Income	2,000,000	0	0
Net Gains (Losses) Recognized in Other Income(a)	0	0	0
Other Income [Member] \| Foreign Exchange Contract [Member] \| Net Investment Hedges [Member]
Derivatives, Fair Value [Line Items]
Net Gains (Losses) Recognized in OCI	19,000,000	(17,000,000)	(2,000,000)
Net Gains (Losses) Reclassified From OCI Into Income	31,000,000	0	0
Net Gains (Losses) Recognized in Other Income(a)	$ 0	$ 0	$ 0

Amount of increase (decrease) in the fair value of derivatives recognized in the income statement.

Reference 1: http://www.xbrl.org/2009/role/commonPracticeRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 815
-SubTopic 10
-Section 50
-Paragraph 4A
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Amount, before tax and reclassification, of gain (loss) from derivative instrument designated and qualifying cash flow hedge included in assessment of hedge effectiveness.

+ References

Reference 1: http://www.xbrl.org/2003/role/disclosureRef
-Publisher FASB
-Name Accounting Standards Codification
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Amount, after tax, of reclassification of gain (loss) from accumulated other comprehensive income (AOCI) for derivative instrument designated and qualifying as cash flow hedge included in assessment of hedge effectiveness.

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