Stockholders' Equity (Summary of Purchases of Common Stock) (Details) - USD ($) $ / shares in Units, shares in Thousands, $ in Millions	3 Months Ended				12 Months Ended
	Mar. 31, 2024	Dec. 31, 2023	Jun. 30, 2023	Mar. 31, 2023	Dec. 31, 2023	Dec. 31, 2022	Dec. 31, 2021
Three Billion Dollar Share Repurchase Program Closed Member
Stockholders Equity [Line Items]
Total Number of Shares Purchased	4,428	5,465	3,795	10,090	19,350	11,708	13,983
Dollar Value of Shares Purchased	$ 193	$ 247	$ 200	$ 545	$ 992	$ 718	$ 589
Average Price Paid per Share	$ 43.47	$ 45.17	$ 52.7	$ 53.96	$ 51.23	$ 61.36	$ 42.15
Share Repurchase Program Open [Member]
Stockholders Equity [Line Items]
Total Number of Shares Purchased	49,469
Dollar Value of Shares Purchased	$ 2,492
Average Price Paid per Share	$ 50.37