New Accounting Standards (Details) - USD ($) $ in Millions	Jan. 01, 2019	Sep. 30, 2019	Jun. 30, 2019	Dec. 31, 2018	Sep. 30, 2018	Jun. 30, 2018	Dec. 31, 2017
New Accounting Pronouncements or Change in Accounting Principle [Line Items]
Operating lease right-of-use asset		$ 596
Operating lease liability		665
Accumulated other comprehensive income (loss)		$ 144	$ 99	$ (252)	$ (304)	$ (278)	$ (152)
ASU 2016-02 [Member]
New Accounting Pronouncements or Change in Accounting Principle [Line Items]
Operating lease right-of-use asset	$ 596
Operating lease liability	662
ASU 2017-12 [Member]
New Accounting Pronouncements or Change in Accounting Principle [Line Items]
Fair value of securities transferred from held to maturity	8,800
Accumulated other comprehensive income (loss)	$ 19