Investments - Summary of Cost and Carrying Value of Equity and Trading Debt Securities (Detail) - USD ($) $ in Millions	Dec. 31, 2019	Dec. 31, 2018
Schedule of Investments [Line Items]
Total trading debt securities, Cost	$ 1,231	$ 1,686
Equity securities at FVTNI, Cost	1,769	1,016
Total trading debt, Carrying Value	1,249	1,660
Equity securities at FVTNI, Carrying Value	1,926	1,021
Corporate Debt [Member]
Schedule of Investments [Line Items]
Total trading debt securities, Cost	822	800
Total trading debt, Carrying Value	844	798
Government Debt [Member]
Schedule of Investments [Line Items]
Total trading debt securities, Cost	268	771
Total trading debt, Carrying Value	269	756
Asset/Mortgage-Backed Debt [Member]
Schedule of Investments [Line Items]
Total trading debt securities, Cost	141	115
Total trading debt, Carrying Value	136	106
Deferred Compensation Plan Fund [Member]
Schedule of Investments [Line Items]
Equity securities at FVTNI, Cost	6	21
Equity securities at FVTNI, Carrying Value	23	34
Equity Securities/Multi-Asset Mutual Funds [Member]
Schedule of Investments [Line Items]
Equity securities at FVTNI, Cost	1,763	995
Equity securities at FVTNI, Carrying Value	$ 1,903	$ 987

Amount of investment in equity security measured at fair value with change in fair value recognized in net income (FV-NI).

Reference 1: http://www.xbrl.org/2003/role/disclosureRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 825
-SubTopic 10
-Section 45
-Paragraph 1A
-URI http://asc.fasb.org/extlink&oid=99377092&loc=SL75136599-209740

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Amount of investment in debt security measured at fair value with change in fair value recognized in net income (trading).

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Reference 1: http://www.xbrl.org/2003/role/disclosureRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 320
-SubTopic 10
-Section 45
-Paragraph 1
-Subparagraph (b)
-URI http://asc.fasb.org/extlink&oid=118954083&loc=d3e26610-111562

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