Debt (Carrying Value Of Long-Term Debt) (Details) - USD ($) $ in Millions	Dec. 31, 2020	Nov. 23, 2020	Aug. 17, 2020	May 05, 2020	Dec. 31, 2019	Aug. 15, 2019	Mar. 02, 2018	May 12, 2015	Oct. 09, 2012
Debt Instrument [Line Items]
Long-term debt	$ 20,035				$ 19,385
Current portion of long-term debt	(700)				(1,598)
Long-term debt, less current portion	19,335				17,787
Senior Unsecured Notes [Member] | 2.500% due 2020 [Member]
Debt Instrument [Line Items]
Long-term debt	$ 0				$ 899
Interest rate on long-term debt	2.50%	2.50%			2.50%
Senior Unsecured Notes [Member] | 4.350%, due 2020 [Member]
Debt Instrument [Line Items]
Long-term debt	$ 0				$ 699
Interest rate on long-term debt	4.35%		4.35%		4.35%
Senior Unsecured Notes [Member] | 3.700%, due 2021 [Member]
Debt Instrument [Line Items]
Long-term debt	$ 700				$ 699
Interest rate on long-term debt	3.70%				3.70%
Senior Unsecured Notes [Member] | 2.950% due 2022 [Member]
Debt Instrument [Line Items]
Long-term debt	$ 749				$ 747
Interest rate on long-term debt	2.95%				2.95%
Senior Unsecured Notes [Member] | 3.125%, due 2022 [Member]
Debt Instrument [Line Items]
Long-term debt	$ 848				$ 847
Interest rate on long-term debt	3.125%				3.125%
Senior Unsecured Notes [Member] | 3.300%, due 2023 [Member]
Debt Instrument [Line Items]
Long-term debt	$ 1,027				$ 1,013
Interest rate on long-term debt	3.30%				3.30%
Senior Unsecured Notes [Member] | 3.350% due 2024 [Member]
Debt Instrument [Line Items]
Long-term debt	$ 847				$ 846
Interest rate on long-term debt	3.35%				3.35%
Senior Unsecured Notes [Member] | 3.500%, due 2024 [Member]
Debt Instrument [Line Items]
Long-term debt	$ 796				$ 795
Interest rate on long-term debt	3.50%				3.50%
Senior Unsecured Notes [Member] | 2.375%, due 2025 [Member]
Debt Instrument [Line Items]
Long-term debt	$ 1,253				$ 845
Interest rate on long-term debt	2.375%
Senior Unsecured Notes [Member] | 3.650% due 2027 [Member]
Debt Instrument [Line Items]
Long-term debt	$ 1,591				$ 1,590
Interest rate on long-term debt	3.65%				3.65%
Senior Unsecured Notes [Member] | 4.101%, due 2028 [Member]
Debt Instrument [Line Items]
Long-term debt	$ 1,257				$ 1,253
Interest rate on long-term debt	4.101%				4.101%
Senior Unsecured Notes [Member] | 2.875%, due 2029 [Member]
Debt Instrument [Line Items]
Long-term debt	$ 819				$ 819
Interest rate on long-term debt	2.875%
Senior Unsecured Notes [Member] | 2.250%, due 2030 [Member]
Debt Instrument [Line Items]
Long-term debt	$ 1,089				0
Interest rate on long-term debt	2.25%			2.25%
Senior Unsecured Notes [Member] | 5.950%, due 2034 [Member]
Debt Instrument [Line Items]
Long-term debt	$ 334				$ 334
Interest rate on long-term debt	5.95%				5.95%
Senior Unsecured Notes [Member] | 5.850%, due 2036 [Member]
Debt Instrument [Line Items]
Long-term debt	$ 396				$ 396
Interest rate on long-term debt	5.85%				5.85%
Senior Unsecured Notes [Member] | 6.375%, due 2037 [Member]
Debt Instrument [Line Items]
Long-term debt	$ 366				$ 366
Interest rate on long-term debt	6.375%				6.375%
Senior Unsecured Notes [Member] | 5.800%, due 2040 [Member]
Debt Instrument [Line Items]
Long-term debt	$ 114				$ 124
Interest rate on long-term debt	5.80%				5.80%
Senior Unsecured Notes [Member] | 4.625%, due 2042 [Member]
Debt Instrument [Line Items]
Long-term debt	$ 873				$ 888
Interest rate on long-term debt	4.625%				4.625%
Senior Unsecured Notes [Member] | 4.650%, due 2043 [Member]
Debt Instrument [Line Items]
Long-term debt	$ 978				$ 987
Interest rate on long-term debt	4.65%				4.65%
Senior Unsecured Notes [Member] | 4.650%, due 2044 [Member]
Debt Instrument [Line Items]
Long-term debt	$ 779				$ 792
Interest rate on long-term debt	4.65%				4.65%
Senior Unsecured Notes [Member] | 5.100%, due 2044 [Member]
Debt Instrument [Line Items]
Long-term debt	$ 565				$ 594
Interest rate on long-term debt	5.10%				5.10%
Senior Unsecured Notes [Member] | 4.375% due 2047 [Member]
Debt Instrument [Line Items]
Long-term debt	$ 1,387				$ 1,386
Interest rate on long-term debt	4.375%				4.375%
Senior Unsecured Notes [Member] | 4.550%, due 2048 [Member]
Debt Instrument [Line Items]
Long-term debt	$ 839				$ 838
Interest rate on long-term debt	4.55%				4.55%
Senior Unsecured Notes [Member] | 3.700%, due 2049 [Member]
Debt Instrument [Line Items]
Long-term debt	$ 811				$ 811
Interest rate on long-term debt	3.70%
Senior Unsecured Notes [Member] | 3.125% due 2050 [Member]
Debt Instrument [Line Items]
Long-term debt	$ 987				0
Interest rate on long-term debt	3.125%			3.125%
Senior Unsecured Notes [Member] | 4.850%, due 2054 [Member]
Debt Instrument [Line Items]
Long-term debt	$ 247				$ 247
Interest rate on long-term debt	4.85%				4.85%
Senior Unsecured Notes [Member] | 2.250%, due 2019 [Member]
Debt Instrument [Line Items]
Interest rate on long-term debt						2.25%
Remarketable Subordinated Notes [Member] | 4.101%, due 2028 [Member]
Debt Instrument [Line Items]
Interest rate on long-term debt							4.101%
Remarketable Subordinated Notes [Member] | 4.550%, due 2048 [Member]
Debt Instrument [Line Items]
Interest rate on long-term debt							4.55%
Remarketable Subordinated Notes [Member] | 1.900%, due 2028 [Member]
Debt Instrument [Line Items]
Interest rate on long-term debt								1.90%
Senior Convertible Debentures [Member] | 2.750%, due 2042 [Member]
Debt Instrument [Line Items]
Long-term debt	$ 108				$ 145
Interest rate on long-term debt	2.75%				2.75%				2.75%
Surplus Notes [Member] | 9.000%, due 2027 [Member]
Debt Instrument [Line Items]
Long-term debt	$ 25				$ 25
Interest rate on long-term debt	9.00%				9.00%
Commercial Paper [Member]
Debt Instrument [Line Items]
Commercial paper	$ 250				$ 400