Fair Value Measurement and Fair Value of Financial Instruments - Financial Assets Measured at Fair Value on Nonrecurring Basis (Details) - USD ($) $ in Millions	3 Months Ended
	Mar. 31, 2020	Mar. 31, 2019	Dec. 31, 2019
Loans:
Goodwill	$ 1,764		$ 1,764
Other assets:
Other Assets	11,791		$ 10,200
Total Gains Losses on Assets	(52)	$ (20)
Fair Value Measurements, Nonrecurring
Other assets:
Total	486	353
Fair Value Measurements, Nonrecurring | Level 1
Other assets:
Total	0	0
Fair Value Measurements, Nonrecurring | Level 2
Other assets:
Total	0	0
Fair Value Measurements, Nonrecurring | Level 3
Other assets:
Total	$ 486	$ 353