Debt (Narrative) (Details) - USD ($)	3 Months Ended		9 Months Ended
	Sep. 30, 2020	Sep. 30, 2019	Sep. 30, 2020	Sep. 30, 2019	Dec. 31, 2019
Line of Credit Facility [Line Items]
Face value of debt	$ 20,330,000,000		$ 20,330,000,000		$ 19,230,000,000
Loss on extinguishment of debt	$ 23,000,000	$ 0	$ 126,000,000	$ 0
5.875% Junior Subordinated Debentures due 2057 [Member]
Line of Credit Facility [Line Items]
Stated interest rate	5.875%		5.875%
5.875% Junior Subordinated Debentures due 2057 [Member] | London Interbank Offered Rate (LIBOR) [Member]
Line of Credit Facility [Line Items]
Basis spread on variable rate			3.895%
6.25% Junior Subordinated Debentures due 2057 [Member]
Line of Credit Facility [Line Items]
Stated interest rate	6.25%		6.25%
6.25% Junior Subordinated Debentures due 2057 [Member] | London Interbank Offered Rate (LIBOR) [Member]
Line of Credit Facility [Line Items]
Basis spread on variable rate			3.899%
Senior Notes [Member]
Line of Credit Facility [Line Items]
Face value of debt	$ 4,500,000,000		$ 4,500,000,000
Debt redeemed	340,000,000		$ 340,000,000
Payments for debt redemption	$ 357,000,000
Senior Notes [Member] | Minimum [Member]
Line of Credit Facility [Line Items]
Stated interest rate	4.20%		4.20%
Senior Notes [Member] | Maximum [Member]
Line of Credit Facility [Line Items]
Stated interest rate	4.95%		4.95%
Senior Notes and Junior Subordinated Debentures [Member]
Line of Credit Facility [Line Items]
Debt redeemed	$ 2,770,000,000		$ 2,770,000,000
Payments for debt redemption			$ 2,880,000,000