Segment Information (Premiums, Fees and Other Revenues by US and Foreign Operations) (Details) - USD ($) $ in Millions	12 Months Ended
	Dec. 31, 2020	Dec. 31, 2019	Dec. 31, 2018
Segment Reporting Information [Line Items]
Premiums, Fees & Other Revenues	$ 49,486	$ 49,680	$ 51,222
UNITED STATES
Segment Reporting Information [Line Items]
Premiums, Fees & Other Revenues	34,717	34,433	36,078
Japan
Segment Reporting Information [Line Items]
Premiums, Fees & Other Revenues	6,750	6,608	6,435
Other Foreign
Segment Reporting Information [Line Items]
Premiums, Fees & Other Revenues	$ 8,019	$ 8,639	$ 8,709