Debt (Carrying Value Of Long-Term Debt) (Details) - USD ($) $ in Millions	Dec. 31, 2018	Dec. 31, 2017	May 12, 2015	Oct. 09, 2012
Debt Instrument [Line Items]
Long-term debt	$ 18,066	$ 18,657
Current portion of long-term debt	(849)	(1,275)
Long-term debt, less current portion	17,217	17,382
Senior Unsecured Notes [Member] | 1.875%, due 2018 [Member]
Debt Instrument [Line Items]
Long-term debt	$ 0	$ 625
Interest rate on long-term debt	1.875%	1.875%
Senior Unsecured Notes [Member] | 2.300%, due 2018 [Member]
Debt Instrument [Line Items]
Long-term debt	$ 0	$ 649
Interest rate on long-term debt	2.30%	2.30%
Senior Unsecured Notes [Member] | 2.250%, due 2019 [Member]
Debt Instrument [Line Items]
Long-term debt	$ 849	$ 847
Interest rate on long-term debt	2.25%	2.25%
Senior Unsecured Notes [Member] | 2.500% due 2020 [Member]
Debt Instrument [Line Items]
Long-term debt	$ 897	$ 895
Interest rate on long-term debt	2.50%	2.50%
Senior Unsecured Notes [Member] | 4.350%, due 2020 [Member]
Debt Instrument [Line Items]
Long-term debt	$ 688	$ 693
Interest rate on long-term debt	4.35%	4.35%
Senior Unsecured Notes [Member] | 3.700%, due 2021 [Member]
Debt Instrument [Line Items]
Long-term debt	$ 698	$ 698
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	$ 747	$ 746
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	$ 846	$ 845
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	$ 1,000	$ 994
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	$ 846	$ 845
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	$ 794	$ 793
Interest rate on long-term debt	3.50%	3.50%
Senior Unsecured Notes [Member] | 3.650% due 2027 [Member]
Debt Instrument [Line Items]
Long-term debt	$ 1,589	$ 1,589
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	$ 1,250	$ 0
Interest rate on long-term debt	4.101%	0.00%
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	$ 124	$ 123
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	$ 887	$ 887
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	$ 986	$ 986
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	$ 791	$ 791
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	$ 594	$ 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	$ 1,386	$ 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	$ 838	$ 0
Interest rate on long-term debt	4.55%	4.55%
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%
Remarketable Subordinated Notes [Member] | 1.900%, due 2028 [Member]
Debt Instrument [Line Items]
Long-term debt	$ 0	$ 1,239
Interest rate on long-term debt	1.90%	1.90%	1.90%
Senior Convertible Debentures [Member] | 2.750%, due 2042 [Member]
Debt Instrument [Line Items]
Long-term debt	$ 191	$ 260
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	$ 697	$ 804