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		9 Months Ended
	Sep. 30, 2020	Sep. 30, 2019	Sep. 30, 2020	Sep. 30, 2019	Dec. 31, 2019
Loans:
Goodwill	$ 1,407		$ 1,407		$ 1,764
Other assets:
Other Assets	9,481		9,481		$ 10,200
Total Gains Losses on Assets	(403)	$ (1,637)	(525)	$ (1,655)
Gains Losses on Other Assets			(70)	(21)
Gains Losses On Impaired Loans			(98)	(20)
Fair Value Measurements, Nonrecurring
Fair value measurements
Impaired Financing Receivable, Recorded Investment	106	36	106	36
Other assets:
Other Assets	101	260	101	260
Total	1,614	2,060	1,614	2,060
Fair Value Measurements, Nonrecurring | Level 1
Other assets:
Total	0	0	0	0
Fair Value Measurements, Nonrecurring | Level 2
Other assets:
Total	0	0	0	0
Fair Value Measurements, Nonrecurring | Level 3
Fair value measurements
Impaired Financing Receivable, Recorded Investment	106	36	106	36
Other assets:
Other Assets	101	260	101	260
Total	1,614	2,060	1,614	2,060
Loans and Finance Receivables
Other assets:
Total Gains Losses on Assets	(31)	(17)
Loans and Finance Receivables | Fair Value Measurements, Nonrecurring | Level 1
Fair value measurements
Impaired Financing Receivable, Recorded Investment	0	0	0	0
Loans and Finance Receivables | Fair Value Measurements, Nonrecurring | Level 2
Fair value measurements
Impaired Financing Receivable, Recorded Investment	0	0	0	0
Goodwill [Member]
Other assets:
Total Gains Losses on Assets	(357)	(1,614)	(357)	(1,614)
Goodwill [Member] | Fair Value Measurements, Nonrecurring
Other assets:
Total	1,407	1,764	1,407	1,764
Goodwill [Member] | Fair Value Measurements, Nonrecurring | Level 3
Other assets:
Total	1,407	1,764	1,407	1,764
Other Assets
Other assets:
Total Gains Losses on Assets	(15)	(6)
Other Assets | Fair Value Measurements, Nonrecurring | Level 1
Other assets:
Other Assets	0	0	0	0
Other Assets | Fair Value Measurements, Nonrecurring | Level 2
Other assets:
Other Assets	$ 0	$ 0	$ 0	$ 0