Summary of effects of initial adoption of ASU 2016-01, ASU 2018-02 and ASC 606 (Detail) - USD ($) $ in Millions	Dec. 31, 2019	Dec. 31, 2018	Jan. 01, 2018	Dec. 31, 2017	Dec. 31, 2016
New Accounting Pronouncements or Change in Accounting Principle [Line Items]
Accumulated other comprehensive income	$ (5,243)	$ (5,015)
Retained earnings	402,493	321,112
Total shareholders’ equity	$ 428,563	$ 352,500		$ 351,954	$ 285,428
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)