Commercial Paper and Long-Term Debt (Commercial Paper and Long-Term Debt) (Details) (USD $) In Millions, unless otherwise specified	Dec. 31, 2011	Dec. 31, 2010
Par Value	$ 11,860	$ 11,495
Carrying Value	11,638	11,142
Fair Value	13,149	11,833
Commercial Paper [Member]
Par Value	0	930
Carrying Value	0	930
Fair Value	0	930
Senior Unsecured Floating-rate Notes Due February 2011 [Member]
Par Value	0	250
Carrying Value	0	250
Fair Value	0	250
5.3% Senior Unsecured Notes Due March 2011 [Member]
Interest rate	5.30%
Par Value	0	705
Carrying Value	0	712
Fair Value	0	711
5.5% Senior Unsecured Notes Due November 2012 [Member]
Interest rate	5.50%
Par Value	352	352
Carrying Value	363	372
Fair Value	366	377
4.9% Senior Unsecured Notes Due February 2013 [Member]
Interest rate	4.90%
Par Value	534	534
Carrying Value	540	541
Fair Value	556	568
4.9% Senior Unsecured Notes Due April 2013 [Member]
Interest rate	4.90%
Par Value	409	409
Carrying Value	421	425
Fair Value	427	437
4.8% Senior Unsecured Notes Due February 2014 [Member]
Interest rate	4.80%
Par Value	172	172
Carrying Value	184	186
Fair Value	185	184
5.0% Senior Unsecured Notes Due August 2014 [Member]
Interest rate	5.00%
Par Value	389	389
Carrying Value	423	425
Fair Value	424	423
4.9% Senior Unsecured Notes Due March 2015 [Member]
Interest rate	4.90%
Par Value	416	416
Carrying Value	458	456
Fair Value	460	444
5.4% Senior Unsecured Notes Due March 2016 [Member]
Interest rate	5.40%
Par Value	601	601
Carrying Value	678	666
Fair Value	689	661
1.9% of Senior Unsecured Notes Due November 2016 [Member]
Interest rate	1.90%
Par Value	400	0
Carrying Value	397	0
Fair Value	400	0
5.4% Senior Unsecured Notes Due November 2016 [Member]
Interest rate	5.40%
Par Value	95	95
Carrying Value	95	95
Fair Value	110	105
6.0% Senior Unsecured Notes Due June 2017 [Member]
Interest rate	6.00%
Par Value	441	441
Carrying Value	499	484
Fair Value	518	491
6.0% Senior Unsecured Notes Due November 2017 [Member]
Interest rate	6.00%
Par Value	156	156
Carrying Value	173	167
Fair Value	183	174
6.0% Senior Unsecured Notes Due February 2018 [Member]
Interest rate	6.00%
Par Value	1,100	1,100
Carrying Value	1,123	1,065
Fair Value	1,308	1,249
3.9% Senior Unsecured Notes Due October 2020 [Member]
Interest rate	3.90%
Par Value	450	450
Carrying Value	442	413
Fair Value	478	429
4.7% Senior Unsecured Notes Due February 2021 [Member]
Interest rate	4.70%
Par Value	400	0
Carrying Value	419	0
Fair Value	450	0
3.4% of Senior Unsecured Notes Due November 2021 [Member]
Interest rate	3.40%
Par Value	500	0
Carrying Value	497	0
Fair Value	517	0
Zero Coupon Senior Unsecured Notes Due November 2022 [Member]
Par Value	1,095	1,095
Carrying Value	619	588
Fair Value	696	677
5.8% Senior Unsecured Notes Due March 2036 [Member]
Interest rate	5.80%
Par Value	850	850
Carrying Value	844	844
Fair Value	1,017	862
6.5% Senior Unsecured Notes Due June 2037 [Member]
Interest rate	6.50%
Par Value	500	500
Carrying Value	495	495
Fair Value	636	552
6.6% Senior Unsecured Notes Due November 2037 [Member]
Interest rate	6.60%
Par Value	650	650
Carrying Value	645	645
Fair Value	834	729
6.9% Senior Unsecured Notes Due February 2038 [Member]
Interest rate	6.90%
Par Value	1,100	1,100
Carrying Value	1,084	1,085
Fair Value	1,475	1,281
5.7% Senior Unsecured Notes Due October 2040 [Member]
Interest rate	5.70%
Par Value	300	300
Carrying Value	298	298
Fair Value	359	299
6.0% Senior Unsecured Notes Due February 2041 [Member]
Interest rate	6.00%
Par Value	350	0
Carrying Value	348	0
Fair Value	430	0
4.6% of Senior Unsecured Notes Due November 2041 [Member]
Interest rate	4.60%
Par Value	600	0
Carrying Value	593	0
Fair Value	$ 631	$ 0