Investments (Collectively Significant Equity Method Investments - Narrative) (Details) - USD ($) $ in Millions	3 Months Ended								12 Months Ended
	Dec. 31, 2020	Sep. 30, 2020	Jun. 30, 2020	Mar. 31, 2020	Dec. 31, 2019	Sep. 30, 2019	Jun. 30, 2019	Mar. 31, 2019	Dec. 31, 2020	Dec. 31, 2019	Dec. 31, 2018
Schedule of Equity Method Investments [Line Items]
Equity Method Investments	$ 17,900								$ 17,900
Unfunded Commitments For Investments Accounted For Under Equity Method	8,000								8,000
Assets	795,146				$ 740,463				795,146	$ 740,463
Total Liabilities	720,329				674,081				720,329	674,081
Net income (loss)	158	$ 709	$ 150	$ 4,401	588	$ 2,190	$ 1,746	$ 1,385	$ 5,418	$ 5,909	$ 5,128
Aggregate Net Income Exceeded Stated Percentage Of Pre Tax Income (Loss) From Continuing Operations									10.00%	10.00%
Equity Method Investment, Nonconsolidated Investee or Group of Investees [Member]
Schedule of Equity Method Investments [Line Items]
Assets	704,500				585,300				$ 704,500	$ 585,300
Total Liabilities	$ 99,400				$ 86,100				99,400	86,100
Net income (loss)									$ 41,600	$ 47,000	$ 52,500