Summary of effects of initial adoption of ASU 2016-01, ASU 2018-02 and ASC 606 (Detail) - USD ($) $ in Millions	Jun. 30, 2019	Mar. 31, 2019	Dec. 31, 2018	Jun. 30, 2018	Mar. 31, 2018	Jan. 01, 2018	Dec. 31, 2017
New Accounting Pronouncements or Change in Accounting Principle [Line Items]
Accumulated other comprehensive income	$ (4,678)		$ (5,015)
Retained earnings	356,846		321,112
Total shareholders’ equity	$ 386,391	$ 372,591	$ 352,500	$ 361,758	$ 351,052		$ 351,954
ASU 2016-01 [Member]
New Accounting Pronouncements or Change in Accounting Principle [Line Items]
Accumulated other comprehensive income						$ (61,459)
Retained earnings						61,459
ASU 2018-02 [Member]
New Accounting Pronouncements or Change in Accounting Principle [Line Items]
Accumulated other comprehensive income						84
Retained earnings						(84)
ASC 606 [Member]
New Accounting Pronouncements or Change in Accounting Principle [Line Items]
Retained earnings						(70)
Total shareholders’ equity						(70)
Adjustments for New Accounting Pronouncements [Member]
New Accounting Pronouncements or Change in Accounting Principle [Line Items]
Accumulated other comprehensive income						(61,375)
Retained earnings						61,305
Total shareholders’ equity						$ (70)