10-K Debt (Narrative) (Details) - USD ($) $ in Millions			3 Months Ended	12 Months Ended
	Mar. 15, 2023	May 15, 2021	Mar. 31, 2023	Dec. 31, 2023	Dec. 31, 2022	Dec. 31, 2021	Feb. 08, 2023	Jan. 17, 2023	Dec. 01, 2022	Nov. 04, 2022	May 16, 2022	Apr. 29, 2022	Mar. 17, 2021
Debt Instrument [Line Items]
Repayments of Long-term Debt				$ 1,909	$ 1,899	$ 1,068
(Loss) gain on extinguishment of debt				0	0	(21)
Interest Paid, Including Capitalized Interest, Operating and Investing Activities				1,032	878	822
Long-Term Debt, Maturity, Year One				1,649
Long-Term Debt, Maturity, Year Two				1,650
Long-Term Debt, Maturity, Year Three				1,243
Long-Term Debt, Maturity, Year Four				1,595
Long-Term Debt, Maturity, Year Five				1,236
Long-Term Debt, Maturity, after Year Five				17,522
Other senior unsecured notes
Debt Instrument [Line Items]
Extinguishment of Debt, Amount						52
Remarketable subordinated notes tendered, cash payment						67
(Loss) gain on extinguishment of debt						(15)
Commercial Paper
Debt Instrument [Line Items]
Commercial paper authorized				4,000
Commercial paper				$ 0	$ 0
Four Point Nine Zero Zero Percent Due Two Thousand Twenty Six | Senior Unsecured Notes [Member]
Debt Instrument [Line Items]
Debt instrument interest rate				4.90%			4.90%
Debt Instrument, Face Amount							$ 500
Four Point Seven Five Zero Percent Due Two Thousand Thirty Three | Senior Unsecured Notes [Member]
Debt Instrument [Line Items]
Debt instrument interest rate				4.75%			4.75%
Debt Instrument, Face Amount							$ 1,000
Five Point One Two Five Percent Due Two Thousand Fifty Three | Senior Unsecured Notes [Member]
Debt Instrument [Line Items]
Debt instrument interest rate				5.125%			5.125%
Debt Instrument, Face Amount							$ 1,100
Two Point Nine Five Zero Percent Due Two Thousand Twenty Two | Senior Unsecured Notes [Member]
Debt Instrument [Line Items]
Debt instrument interest rate									2.95%
Debt instruments, repurchased face amount									$ 750
Five Point Three Five Zero Percent Due Two Thousand Twenty Five | Senior Unsecured Notes [Member]
Debt Instrument [Line Items]
Debt instrument interest rate				5.35%						5.35%
Debt Instrument, Face Amount										$ 400
Five Point Five Zero Zero Percent Due Two Thousand Thirty Two | Senior Unsecured Notes [Member]
Debt Instrument [Line Items]
Debt instrument interest rate				5.50%						5.50%
Debt Instrument, Face Amount										$ 650
Six Point One Zero Zero Percent Due Two Thousand Fifty Two | Senior Unsecured Notes [Member]
Debt Instrument [Line Items]
Debt instrument interest rate				6.10%						6.10%
Debt Instrument, Face Amount										$ 750
Three Point One Two Five Percent Due Two Thousand Twenty Two | Senior Unsecured Notes [Member]
Debt Instrument [Line Items]
Debt instrument interest rate											3.125%
Debt instruments, repurchased face amount											$ 850
Four Point One Zero Percent Due Two Thousand Thirty Two | Senior Unsecured Notes [Member]
Debt Instrument [Line Items]
Debt instrument interest rate				4.10%								4.10%
Debt Instrument, Face Amount												$ 600
Four Point Five Five Zero Due Two Thousand Fifty Two | Senior Unsecured Notes [Member]
Debt Instrument [Line Items]
Debt instrument interest rate				4.55%								4.55%
Debt Instrument, Face Amount												$ 700
Zero Point Four Five Zero Percent Due Two Thousand Twenty Three | Senior Unsecured Notes [Member]
Debt Instrument [Line Items]
Debt instrument interest rate	0.45%				0.45%								0.45%
Debt Instrument, Face Amount													$ 500
Debt instruments, repurchased face amount	$ 500
One Point Five Zero Zero Percent Due Two Thousand Twenty Six | Senior Unsecured Notes [Member]
Debt Instrument [Line Items]
Debt instrument interest rate				1.50%									1.50%
Debt Instrument, Face Amount													$ 750
Two Point Five Five Zero Percent Due Two Thousand Thirty One | Senior Unsecured Notes [Member]
Debt Instrument [Line Items]
Debt instrument interest rate				2.55%									2.55%
Debt Instrument, Face Amount													$ 1,000
Three Point Six Zero Zero Percent Due Two Thousand Fifty One | Senior Unsecured Notes [Member]
Debt Instrument [Line Items]
Debt instrument interest rate				3.60%									3.60%
Debt Instrument, Face Amount													$ 1,250
Two Point Two Five Zero Percent Due Two Thousand Thirty | Senior Unsecured Notes [Member]
Debt Instrument [Line Items]
Debt instrument interest rate				2.25%
Three Point One Two Five Percent Due Two Thousand Fifty | Senior Unsecured Notes [Member]
Debt Instrument [Line Items]
Debt instrument interest rate				3.125%
Two Point Seven Five Zero Percent Due Two Thousand Forty Two | Senior Convertible Debenture [Member]
Debt Instrument [Line Items]
Debt instrument interest rate				2.75%	2.75%
Debt Instrument, Redemption Period, End Date	Mar. 15, 2023
Debt Instrument, Redemption Price, Percentage	100.00%
Debt Conversion Debt Principal Amount			$ 59		$ 41	54
Repayments of Long-term Debt	$ 5		$ 404		299	302
(Loss) gain on extinguishment of debt						(6)
Amoritization of bridge facility fees				$ 0	2	4
Interest Expense, Debt, Excluding Amortization				0	2	3
Amortization of Debt Discount (Premium)				0	$ 0	$ 1
Three Point Three Zero Zero Percent Due Two Thousand Twenty Three | Senior Unsecured Notes [Member]
Debt Instrument [Line Items]
Debt instrument interest rate					3.30%			3.30%
Debt instruments, repurchased face amount								$ 1,000
Three Point Seven Zero Zero Percent Due Two Thousand Twenty One | Senior Unsecured Notes [Member]
Debt Instrument [Line Items]
Debt instrument interest rate		3.70%
Debt, Redemption amount		$ 700
Debt Instrument, Redemption, Description		at a redemption price equal to 100% of the aggregate principal amount of the notes being redeemed, plus accrued and unpaid interest.
Revolving Credit Facility [Member] | 5-Year Facility
Debt Instrument [Line Items]
Line of Credit Facility, Maximum Borrowing Capacity				4,000
Federal Home Loan Bank Advances [Member]
Debt Instrument [Line Items]
Short-term FHLB borrowings outstanding				$ 225	$ 265
Debt instrument interest rate				5.46%
Revolving Credit Facility [Member]
Debt Instrument [Line Items]
Covenant description				Our ability to borrow under the 5-Year Facility is subject to compliance with certain covenants, including covenants requiring us to maintain a defined debt-to-capital ratio of not more than 60%, subject to increase in certain circumstances set forth in the credit agreement for the 5-Year Facility.
Covenant compliance				As of December 31, 2023, our debt-to-capital ratio, as defined and calculated under the 5-Year Facility, was 38.9%. We do not believe the restrictions contained in our 5-Year Facility covenants materially affect our financial or operating flexibility. As of December 31, 2023, we were in compliance with all of our debt covenants under the 5-Year Facility.