Segment Information (Premiums, Fees and Other Revenues by US and Foreign Operations) (Details) - USD ($) $ in Millions	12 Months Ended
	Dec. 31, 2019	Dec. 31, 2018	Dec. 31, 2017
Segment Reporting Information [Line Items]
Premiums, Fees & Other Revenues	$ 49,680	$ 51,222	$ 45,843
U.S.
Segment Reporting Information [Line Items]
Premiums, Fees & Other Revenues	34,433	36,078	30,971
Japan
Segment Reporting Information [Line Items]
Premiums, Fees & Other Revenues	6,608	6,435	6,444
Other Foreign
Segment Reporting Information [Line Items]
Premiums, Fees & Other Revenues	$ 8,639	$ 8,709	$ 8,428